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 $241.66   9.464%   $264.5307   $264.53   $264.55   $264.50  
  Purchase #2 $79.74   4.680%   $83.4718   $83.47   $83.45   $83.50  
  Purchase #3 $218.96   9.872%   $240.5757   $240.58   $240.60   $240.60  
  Purchase #4 $21.98   12.575%   $24.744   $24.74   $24.75   $24.70  
  Purchase #5 $231.31   9.590%   $253.4926   $253.49   $253.50   $253.50  
  Purchase #6 $196.75   5.613%   $207.7936   $207.79   $207.80   $207.80  
  Purchase #7 $113.73   8.841%   $123.7849   $123.78   $123.80   $123.80  
  7 purchase totals = $1,104.13       $1,198.3933   $1,198.38   $1,198.45   $1,198.40