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 $206.69   8.151%   $223.5373   $223.54   $223.55   $223.50  
  Purchase #2 $21.46   13.278%   $24.3095   $24.31   $24.30   $24.30  
  Purchase #3 $183.62   7.431%   $197.2648   $197.26   $197.25   $197.30  
  Purchase #4 $34.93   10.256%   $38.5124   $38.51   $38.50   $38.50  
  Purchase #5 $205.89   9.796%   $226.059   $226.06   $226.05   $226.10  
  Purchase #6 $189.32   4.586%   $198.0022   $198.00   $198.00   $198.00  
  Purchase #7 $214.78   10.853%   $238.0901   $238.09   $238.10   $238.10  
  7 purchase totals = $1,056.69       $1,145.7753   $1,145.77   $1,145.75   $1,145.80