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 $60.36   10.656%   $66.792   $66.79   $66.80   $66.80  
  Purchase #2 $154.70   9.386%   $169.2201   $169.22   $169.20   $169.20  
  Purchase #3 $226.27   6.142%   $240.1675   $240.17   $240.15   $240.20  
  Purchase #4 $249.52   9.499%   $273.2219   $273.22   $273.20   $273.20  
  Purchase #5 $115.70   4.849%   $121.3103   $121.31   $121.30   $121.30  
  Purchase #6 $94.54   13.218%   $107.0363   $107.04   $107.05   $107.00  
  Purchase #7 $26.33   13.863%   $29.9801   $29.98   $30.00   $30.00  
  7 purchase totals = $927.42       $1,007.7282   $1,007.73   $1,007.70   $1,007.70