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 $54.88   10.688%   $60.7456   $60.75   $60.75   $60.70  
  Purchase #2 $89.98   13.862%   $102.453   $102.45   $102.45   $102.50  
  Purchase #3 $48.50   12.366%   $54.4975   $54.50   $54.50   $54.50  
  Purchase #4 $210.35   9.245%   $229.7969   $229.80   $229.80   $229.80  
  Purchase #5 $104.52   10.222%   $115.204   $115.20   $115.20   $115.20  
  Purchase #6 $26.29   12.544%   $29.5878   $29.59   $29.60   $29.60  
  Purchase #7 $166.52   6.769%   $177.7917   $177.79   $177.80   $177.80  
  7 purchase totals = $701.04       $770.0765   $770.08   $770.10   $770.10