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 $24.81   4.449%   $25.9138   $25.91   $25.90   $25.90  
  Purchase #2 $61.33   11.290%   $68.2542   $68.25   $68.25   $68.30  
  Purchase #3 $98.52   10.676%   $109.038   $109.04   $109.05   $109.00  
  Purchase #4 $66.97   13.737%   $76.1697   $76.17   $76.15   $76.20  
  Purchase #5 $39.80   10.735%   $44.0725   $44.07   $44.05   $44.10  
  Purchase #6 $61.33   7.366%   $65.8476   $65.85   $65.85   $65.80  
  Purchase #7 $164.44   6.555%   $175.219   $175.22   $175.20   $175.20  
  7 purchase totals = $517.20       $564.5148   $564.51   $564.45   $564.50