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 $91.96   6.272%   $97.7277   $97.73   $97.75   $97.70  
  Purchase #2 $204.88   5.272%   $215.6813   $215.68   $215.70   $215.70  
  Purchase #3 $47.48   13.294%   $53.792   $53.79   $53.80   $53.80  
  Purchase #4 $90.47   12.774%   $102.0266   $102.03   $102.05   $102.00  
  Purchase #5 $80.41   8.504%   $87.2481   $87.25   $87.25   $87.20  
  Purchase #6 $236.46   11.459%   $263.556   $263.56   $263.55   $263.60  
  Purchase #7 $12.84   3.826%   $13.3313   $13.33   $13.35   $13.30  
  7 purchase totals = $764.50       $833.3630   $833.37   $833.45   $833.30