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 $94.35   3.490%   $97.6428   $97.64   $97.65   $97.60  
  Purchase #2 $149.68   6.710%   $159.7235   $159.72   $159.70   $159.70  
  Purchase #3 $59.46   5.637%   $62.8118   $62.81   $62.80   $62.80  
  Purchase #4 $123.25   10.841%   $136.6115   $136.61   $136.60   $136.60  
  Purchase #5 $160.86   4.353%   $167.8622   $167.86   $167.85   $167.90  
  Purchase #6 $211.42   5.374%   $222.7817   $222.78   $222.80   $222.80  
  Purchase #7 $65.90   6.745%   $70.345   $70.35   $70.35   $70.30  
  7 purchase totals = $864.92       $917.7785   $917.77   $917.75   $917.70