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 $61.98   3.743%   $64.2999   $64.30   $64.30   $64.30  
  Purchase #2 $245.99   11.834%   $275.1005   $275.10   $275.10   $275.10  
  Purchase #3 $187.81   13.357%   $212.8958   $212.90   $212.90   $212.90  
  Purchase #4 $87.63   7.514%   $94.2145   $94.21   $94.20   $94.20  
  Purchase #5 $35.41   4.797%   $37.1086   $37.11   $37.10   $37.10  
  Purchase #6 $234.40   8.545%   $254.4295   $254.43   $254.45   $254.40  
  Purchase #7 $87.87   5.845%   $93.006   $93.01   $93.00   $93.00  
  7 purchase totals = $941.09       $1,031.0548   $1,031.06   $1,031.05   $1,031.00