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 $107.65   7.515%   $115.7399   $115.74   $115.75   $115.70  
  Purchase #2 $193.56   6.609%   $206.3524   $206.35   $206.35   $206.40  
  Purchase #3 $75.92   8.151%   $82.1082   $82.11   $82.10   $82.10  
  Purchase #4 $52.53   6.525%   $55.9576   $55.96   $55.95   $56.00  
  Purchase #5 $6.75   8.785%   $7.343   $7.34   $7.35   $7.30  
  Purchase #6 $54.91   8.395%   $59.5197   $59.52   $59.50   $59.50  
  Purchase #7 $108.75   13.275%   $123.1866   $123.19   $123.20   $123.20  
  7 purchase totals = $600.07       $650.2074   $650.21   $650.20   $650.20