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 $70.43   8.774%   $76.6095   $76.61   $76.60   $76.60  
  Purchase #2 $178.27   13.136%   $201.6875   $201.69   $201.70   $201.70  
  Purchase #3 $112.83   13.537%   $128.1038   $128.10   $128.10   $128.10  
  Purchase #4 $49.27   11.390%   $54.8819   $54.88   $54.90   $54.90  
  Purchase #5 $56.98   11.199%   $63.3612   $63.36   $63.35   $63.40  
  Purchase #6 $247.49   4.263%   $258.0405   $258.04   $258.05   $258.00  
  Purchase #7 $31.74   4.401%   $33.1369   $33.14   $33.15   $33.10  
  7 purchase totals = $747.01       $815.8213   $815.82   $815.85   $815.80