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 $233.33   11.416%   $259.967   $259.97   $259.95   $260.00  
  Purchase #2 $194.27   12.768%   $219.0744   $219.07   $219.05   $219.10  
  Purchase #3 $65.79   11.740%   $73.5137   $73.51   $73.50   $73.50  
  Purchase #4 $47.35   7.750%   $51.0196   $51.02   $51.00   $51.00  
  Purchase #5 $103.74   3.779%   $107.6603   $107.66   $107.65   $107.70  
  Purchase #6 $136.76   13.526%   $155.2582   $155.26   $155.25   $155.30  
  Purchase #7 $95.25   7.365%   $102.2652   $102.27   $102.25   $102.30  
  7 purchase totals = $876.49       $968.7584   $968.76   $968.65   $968.90