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 $238.98   10.568%   $264.2354   $264.24   $264.25   $264.20  
  Purchase #2 $165.75   9.316%   $181.1913   $181.19   $181.20   $181.20  
  Purchase #3 $27.79   6.197%   $29.5121   $29.51   $29.50   $29.50  
  Purchase #4 $162.25   12.695%   $182.8476   $182.85   $182.85   $182.80  
  Purchase #5 $232.25   5.403%   $244.7985   $244.80   $244.80   $244.80  
  Purchase #6 $158.29   13.457%   $179.5911   $179.59   $179.60   $179.60  
  Purchase #7 $208.95   6.348%   $222.2141   $222.21   $222.20   $222.20  
  7 purchase totals = $1,194.26       $1,304.3901   $1,304.39   $1,304.40   $1,304.30