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 $89.34   6.874%   $95.4812   $95.48   $95.50   $95.50  
  Purchase #2 $152.69   3.816%   $158.5167   $158.52   $158.50   $158.50  
  Purchase #3 $111.72   13.619%   $126.9351   $126.94   $126.95   $126.90  
  Purchase #4 $181.97   11.573%   $203.0294   $203.03   $203.05   $203.00  
  Purchase #5 $213.97   11.421%   $238.4075   $238.41   $238.40   $238.40  
  Purchase #6 $39.63   13.134%   $44.835   $44.84   $44.85   $44.80  
  Purchase #7 $65.67   6.519%   $69.951   $69.95   $69.95   $70.00  
  7 purchase totals = $854.99       $937.1559   $937.17   $937.20   $937.10