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 $218.86   13.132%   $247.6007   $247.60   $247.60   $247.60  
  Purchase #2 $124.46   3.331%   $128.6058   $128.61   $128.60   $128.60  
  Purchase #3 $114.89   7.218%   $123.1828   $123.18   $123.20   $123.20  
  Purchase #4 $109.49   7.667%   $117.8846   $117.88   $117.90   $117.90  
  Purchase #5 $20.60   6.855%   $22.0121   $22.01   $22.00   $22.00  
  Purchase #6 $239.55   12.163%   $268.6865   $268.69   $268.70   $268.70  
  Purchase #7 $135.30   11.662%   $151.0787   $151.08   $151.10   $151.10  
  7 purchase totals = $963.15       $1,059.0512   $1,059.05   $1,059.10   $1,059.10