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 $187.44   9.360%   $204.9844   $204.98   $205.00   $205.00  
  Purchase #2 $211.39   8.503%   $229.3645   $229.36   $229.35   $229.40  
  Purchase #3 $198.73   13.611%   $225.7791   $225.78   $225.80   $225.80  
  Purchase #4 $195.88   4.578%   $204.8474   $204.85   $204.85   $204.80  
  Purchase #5 $246.79   11.415%   $274.9611   $274.96   $274.95   $275.00  
  Purchase #6 $87.41   5.873%   $92.5436   $92.54   $92.55   $92.50  
  Purchase #7 $126.36   10.230%   $139.2866   $139.29   $139.30   $139.30  
  7 purchase totals = $1,254.00       $1,371.7667   $1,371.76   $1,371.80   $1,371.80