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 $243.36   13.547%   $276.328   $276.33   $276.35   $276.30  
  Purchase #2 $48.44   13.303%   $54.884   $54.88   $54.90   $54.90  
  Purchase #3 $117.71   6.335%   $125.1669   $125.17   $125.15   $125.20  
  Purchase #4 $149.71   5.641%   $158.1551   $158.16   $158.15   $158.20  
  Purchase #5 $73.30   5.808%   $77.5573   $77.56   $77.55   $77.60  
  Purchase #6 $235.29   4.785%   $246.5486   $246.55   $246.55   $246.50  
  Purchase #7 $84.55   9.145%   $92.2821   $92.28   $92.30   $92.30  
  7 purchase totals = $952.36       $1,030.9220   $1,030.93   $1,030.95   $1,031.00