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 $194.73   4.384%   $203.267   $203.27   $203.25   $203.30  
  Purchase #2 $91.86   10.832%   $101.8103   $101.81   $101.80   $101.80  
  Purchase #3 $110.64   13.855%   $125.9692   $125.97   $125.95   $126.00  
  Purchase #4 $47.69   5.317%   $50.2257   $50.23   $50.25   $50.20  
  Purchase #5 $245.36   11.653%   $273.9518   $273.95   $273.95   $274.00  
  Purchase #6 $91.25   3.151%   $94.1253   $94.13   $94.15   $94.10  
  Purchase #7 $161.82   9.582%   $177.3256   $177.33   $177.35   $177.30  
  7 purchase totals = $943.35       $1,026.6749   $1,026.69   $1,026.70   $1,026.70