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 $228.91   11.214%   $254.58   $254.58   $254.60   $254.60  
  Purchase #2 $137.76   9.150%   $150.365   $150.37   $150.35   $150.40  
  Purchase #3 $198.72   11.668%   $221.9066   $221.91   $221.90   $221.90  
  Purchase #4 $21.54   5.665%   $22.7602   $22.76   $22.75   $22.80  
  Purchase #5 $133.74   9.536%   $146.4934   $146.49   $146.50   $146.50  
  Purchase #6 $208.41   5.249%   $219.3494   $219.35   $219.35   $219.30  
  Purchase #7 $26.49   12.501%   $29.8015   $29.80   $29.80   $29.80  
  7 purchase totals = $955.57       $1,045.2561   $1,045.26   $1,045.25   $1,045.30