Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $144.46   6.334%   $153.6101   $153.61   $153.60   $153.60  
  Purchase #2 $186.29   6.284%   $197.9965   $198.00   $198.00   $198.00  
  Purchase #3 $210.64   10.121%   $231.9589   $231.96   $231.95   $232.00  
  Purchase #4 $248.32   12.468%   $279.2805   $279.28   $279.30   $279.30  
  Purchase #5 $161.65   8.690%   $175.6974   $175.70   $175.70   $175.70  
  Purchase #6 $129.55   5.456%   $136.6182   $136.62   $136.60   $136.60  
  Purchase #7 $114.53   4.689%   $119.9003   $119.90   $119.90   $119.90  
  7 purchase totals = $1,195.44       $1,295.0619   $1,295.07   $1,295.05   $1,295.10