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 $51.49   5.553%   $54.3492   $54.35   $54.35   $54.30  
  Purchase #2 $188.76   8.722%   $205.2236   $205.22   $205.20   $205.20  
  Purchase #3 $242.70   8.682%   $263.7712   $263.77   $263.75   $263.80  
  Purchase #4 $209.26   10.289%   $230.7908   $230.79   $230.80   $230.80  
  Purchase #5 $12.46   13.738%   $14.1718   $14.17   $14.15   $14.20  
  Purchase #6 $157.96   10.793%   $175.0086   $175.01   $175.00   $175.00  
  Purchase #7 $113.74   10.863%   $126.0956   $126.10   $126.10   $126.10  
  7 purchase totals = $976.37       $1,069.4108   $1,069.41   $1,069.35   $1,069.40