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 $237.67   12.549%   $267.4952   $267.50   $267.50   $267.50  
  Purchase #2 $79.52   9.379%   $86.9782   $86.98   $87.00   $87.00  
  Purchase #3 $100.89   6.544%   $107.4922   $107.49   $107.50   $107.50  
  Purchase #4 $104.92   13.654%   $119.2458   $119.25   $119.25   $119.20  
  Purchase #5 $85.93   13.524%   $97.5512   $97.55   $97.55   $97.60  
  Purchase #6 $204.25   13.682%   $232.1955   $232.20   $232.20   $232.20  
  Purchase #7 $163.33   8.427%   $177.0938   $177.09   $177.10   $177.10  
  7 purchase totals = $976.51       $1,088.0519   $1,088.06   $1,088.10   $1,088.10