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 $243.55   4.686%   $254.9628   $254.96   $254.95   $255.00  
  Purchase #2 $177.76   5.869%   $188.1927   $188.19   $188.20   $188.20  
  Purchase #3 $52.72   12.158%   $59.1297   $59.13   $59.15   $59.10  
  Purchase #4 $228.81   10.811%   $253.5466   $253.55   $253.55   $253.50  
  Purchase #5 $33.40   12.332%   $37.5189   $37.52   $37.50   $37.50  
  Purchase #6 $24.77   6.352%   $26.3434   $26.34   $26.35   $26.30  
  Purchase #7 $5.38   8.415%   $5.8327   $5.83   $5.85   $5.80  
  7 purchase totals = $766.39       $825.5268   $825.52   $825.55   $825.40