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 $10.39   3.231%   $10.7257   $10.73   $10.75   $10.70  
  Purchase #2 $245.89   5.393%   $259.1508   $259.15   $259.15   $259.20  
  Purchase #3 $149.89   13.612%   $170.293   $170.29   $170.30   $170.30  
  Purchase #4 $235.57   4.839%   $246.9692   $246.97   $246.95   $247.00  
  Purchase #5 $95.68   5.791%   $101.2208   $101.22   $101.20   $101.20  
  Purchase #6 $224.34   6.586%   $239.115   $239.12   $239.10   $239.10  
  Purchase #7 $6.52   13.794%   $7.4194   $7.42   $7.40   $7.40  
  7 purchase totals = $968.28       $1,034.8939   $1,034.90   $1,034.85   $1,034.90