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 $59.82   5.182%   $62.9199   $62.92   $62.90   $62.90  
  Purchase #2 $218.67   13.164%   $247.4557   $247.46   $247.45   $247.50  
  Purchase #3 $71.88   5.286%   $75.6796   $75.68   $75.70   $75.70  
  Purchase #4 $15.96   9.748%   $17.5158   $17.52   $17.50   $17.50  
  Purchase #5 $232.62   12.735%   $262.2442   $262.24   $262.25   $262.20  
  Purchase #6 $141.47   5.841%   $149.7333   $149.73   $149.75   $149.70  
  Purchase #7 $241.56   3.409%   $249.7948   $249.79   $249.80   $249.80  
  7 purchase totals = $981.98       $1,065.3433   $1,065.34   $1,065.35   $1,065.30