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 $204.62   13.703%   $232.6591   $232.66   $232.65   $232.70  
  Purchase #2 $116.49   10.617%   $128.8577   $128.86   $128.85   $128.90  
  Purchase #3 $226.47   10.473%   $250.1882   $250.19   $250.20   $250.20  
  Purchase #4 $83.82   11.438%   $93.4073   $93.41   $93.40   $93.40  
  Purchase #5 $156.63   8.149%   $169.3938   $169.39   $169.40   $169.40  
  Purchase #6 $238.88   8.562%   $259.3329   $259.33   $259.35   $259.30  
  Purchase #7 $108.92   5.567%   $114.9836   $114.98   $115.00   $115.00  
  7 purchase totals = $1,135.83       $1,248.8226   $1,248.82   $1,248.85   $1,248.90