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 $123.94   6.496%   $131.9911   $131.99   $132.00   $132.00  
  Purchase #2 $80.97   4.462%   $84.5829   $84.58   $84.60   $84.60  
  Purchase #3 $187.64   10.590%   $207.5111   $207.51   $207.50   $207.50  
  Purchase #4 $221.27   13.225%   $250.533   $250.53   $250.55   $250.50  
  Purchase #5 $158.26   5.866%   $167.5435   $167.54   $167.55   $167.50  
  Purchase #6 $180.64   4.682%   $189.0976   $189.10   $189.10   $189.10  
  Purchase #7 $235.51   11.706%   $263.0788   $263.08   $263.10   $263.10  
  7 purchase totals = $1,188.23       $1,294.3380   $1,294.33   $1,294.40   $1,294.30