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 $55.96   5.798%   $59.2046   $59.20   $59.20   $59.20  
  Purchase #2 $201.86   13.453%   $229.0162   $229.02   $229.00   $229.00  
  Purchase #3 $14.60   4.128%   $15.2027   $15.20   $15.20   $15.20  
  Purchase #4 $250.62   3.578%   $259.5872   $259.59   $259.60   $259.60  
  Purchase #5 $24.56   6.463%   $26.1473   $26.15   $26.15   $26.10  
  Purchase #6 $203.96   11.277%   $226.9606   $226.96   $226.95   $227.00  
  Purchase #7 $134.44   10.568%   $148.6476   $148.65   $148.65   $148.60  
  7 purchase totals = $886.00       $964.7662   $964.77   $964.75   $964.70