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 $229.92   7.692%   $247.6054   $247.61   $247.60   $247.60  
  Purchase #2 $174.69   10.111%   $192.3529   $192.35   $192.35   $192.40  
  Purchase #3 $68.59   12.775%   $77.3524   $77.35   $77.35   $77.40  
  Purchase #4 $221.49   6.529%   $235.9511   $235.95   $235.95   $236.00  
  Purchase #5 $49.53   5.650%   $52.3284   $52.33   $52.35   $52.30  
  Purchase #6 $5.98   10.140%   $6.5864   $6.59   $6.60   $6.60  
  Purchase #7 $81.70   7.378%   $87.7278   $87.73   $87.75   $87.70  
  7 purchase totals = $831.90       $899.9044   $899.91   $899.95   $900.00