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 $144.44   11.585%   $161.1734   $161.17   $161.15   $161.20  
  Purchase #2 $249.42   12.188%   $279.8193   $279.82   $279.80   $279.80  
  Purchase #3 $247.31   4.596%   $258.6764   $258.68   $258.70   $258.70  
  Purchase #4 $181.43   8.743%   $197.2924   $197.29   $197.30   $197.30  
  Purchase #5 $180.72   3.387%   $186.841   $186.84   $186.85   $186.80  
  Purchase #6 $177.77   13.194%   $201.225   $201.23   $201.25   $201.20  
  Purchase #7 $230.25   11.168%   $255.9643   $255.96   $255.95   $256.00  
  7 purchase totals = $1,411.34       $1,540.9918   $1,540.99   $1,541.00   $1,541.00