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 $46.78   5.196%   $49.2107   $49.21   $49.20   $49.20  
  Purchase #2 $161.61   10.346%   $178.3302   $178.33   $178.35   $178.30  
  Purchase #3 $183.99   11.481%   $205.1139   $205.11   $205.10   $205.10  
  Purchase #4 $207.67   9.775%   $227.9697   $227.97   $227.95   $228.00  
  Purchase #5 $62.35   6.715%   $66.5368   $66.54   $66.55   $66.50  
  Purchase #6 $135.97   10.302%   $149.9776   $149.98   $150.00   $150.00  
  Purchase #7 $198.53   5.353%   $209.1573   $209.16   $209.15   $209.20  
  7 purchase totals = $996.90       $1,086.2962   $1,086.30   $1,086.30   $1,086.30