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 $75.60   10.732%   $83.7134   $83.71   $83.70   $83.70  
  Purchase #2 $26.28   11.169%   $29.2152   $29.22   $29.20   $29.20  
  Purchase #3 $162.92   8.597%   $176.9262   $176.93   $176.95   $176.90  
  Purchase #4 $192.85   4.367%   $201.2718   $201.27   $201.25   $201.30  
  Purchase #5 $61.52   4.679%   $64.3985   $64.40   $64.40   $64.40  
  Purchase #6 $65.87   13.438%   $74.7216   $74.72   $74.70   $74.70  
  Purchase #7 $124.93   6.212%   $132.6907   $132.69   $132.70   $132.70  
  7 purchase totals = $709.97       $762.9374   $762.94   $762.90   $762.90