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 $68.47   4.668%   $71.6662   $71.67   $71.65   $71.70  
  Purchase #2 $151.98   8.865%   $165.453   $165.45   $165.45   $165.50  
  Purchase #3 $28.30   13.593%   $32.1468   $32.15   $32.15   $32.10  
  Purchase #4 $186.40   8.517%   $202.2757   $202.28   $202.30   $202.30  
  Purchase #5 $61.93   9.734%   $67.9583   $67.96   $67.95   $68.00  
  Purchase #6 $61.53   10.870%   $68.2183   $68.22   $68.20   $68.20  
  Purchase #7 $194.34   12.596%   $218.8191   $218.82   $218.80   $218.80  
  7 purchase totals = $752.95       $826.5374   $826.55   $826.50   $826.60