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 $243.74   8.795%   $265.1769   $265.18   $265.20   $265.20  
  Purchase #2 $236.46   11.118%   $262.7496   $262.75   $262.75   $262.70  
  Purchase #3 $148.28   3.236%   $153.0783   $153.08   $153.10   $153.10  
  Purchase #4 $133.32   4.622%   $139.4821   $139.48   $139.50   $139.50  
  Purchase #5 $244.96   7.601%   $263.5794   $263.58   $263.60   $263.60  
  Purchase #6 $174.36   11.828%   $194.9833   $194.98   $195.00   $195.00  
  Purchase #7 $91.28   4.690%   $95.561   $95.56   $95.55   $95.60  
  7 purchase totals = $1,272.40       $1,374.6106   $1,374.61   $1,374.70   $1,374.70