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 $195.67   5.612%   $206.651   $206.65   $206.65   $206.70  
  Purchase #2 $63.61   9.446%   $69.6186   $69.62   $69.60   $69.60  
  Purchase #3 $65.56   11.259%   $72.9414   $72.94   $72.95   $72.90  
  Purchase #4 $238.26   6.301%   $253.2728   $253.27   $253.25   $253.30  
  Purchase #5 $173.69   9.389%   $189.9978   $190.00   $190.00   $190.00  
  Purchase #6 $25.52   3.106%   $26.3127   $26.31   $26.30   $26.30  
  Purchase #7 $95.86   4.347%   $100.027   $100.03   $100.05   $100.00  
  7 purchase totals = $858.17       $918.8213   $918.82   $918.80   $918.80