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 $190.73   8.543%   $207.0241   $207.02   $207.00   $207.00  
  Purchase #2 $224.81   13.508%   $255.1773   $255.18   $255.20   $255.20  
  Purchase #3 $153.93   8.353%   $166.7878   $166.79   $166.80   $166.80  
  Purchase #4 $197.45   6.839%   $210.9536   $210.95   $210.95   $211.00  
  Purchase #5 $95.88   13.760%   $109.0731   $109.07   $109.05   $109.10  
  Purchase #6 $52.47   10.343%   $57.897   $57.90   $57.90   $57.90  
  Purchase #7 $9.99   6.295%   $10.6189   $10.62   $10.60   $10.60  
  7 purchase totals = $925.26       $1,017.5318   $1,017.53   $1,017.50   $1,017.60