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 $201.84   10.598%   $223.231   $223.23   $223.25   $223.20  
  Purchase #2 $35.35   5.780%   $37.3932   $37.39   $37.40   $37.40  
  Purchase #3 $64.77   9.711%   $71.0598   $71.06   $71.05   $71.10  
  Purchase #4 $101.67   3.536%   $105.2651   $105.27   $105.25   $105.30  
  Purchase #5 $190.53   9.805%   $209.2115   $209.21   $209.20   $209.20  
  Purchase #6 $221.91   7.555%   $238.6753   $238.68   $238.70   $238.70  
  Purchase #7 $137.92   7.375%   $148.0916   $148.09   $148.10   $148.10  
  7 purchase totals = $953.99       $1,032.9275   $1,032.93   $1,032.95   $1,033.00