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 $41.61   10.628%   $46.0323   $46.03   $46.05   $46.00  
  Purchase #2 $69.35   5.214%   $72.9659   $72.97   $72.95   $73.00  
  Purchase #3 $32.30   11.159%   $35.9044   $35.90   $35.90   $35.90  
  Purchase #4 $221.85   11.107%   $246.4909   $246.49   $246.50   $246.50  
  Purchase #5 $124.86   4.619%   $130.6273   $130.63   $130.65   $130.60  
  Purchase #6 $68.33   3.693%   $70.8534   $70.85   $70.85   $70.90  
  Purchase #7 $133.55   12.476%   $150.2117   $150.21   $150.20   $150.20  
  7 purchase totals = $691.85       $753.0859   $753.08   $753.10   $753.10