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 $76.97   10.598%   $85.1273   $85.13   $85.15   $85.10  
  Purchase #2 $130.35   7.224%   $139.7665   $139.77   $139.75   $139.80  
  Purchase #3 $147.36   5.316%   $155.1937   $155.19   $155.20   $155.20  
  Purchase #4 $225.86   9.853%   $248.114   $248.11   $248.10   $248.10  
  Purchase #5 $147.82   13.431%   $167.6737   $167.67   $167.65   $167.70  
  Purchase #6 $244.50   12.476%   $275.0038   $275.00   $275.00   $275.00  
  Purchase #7 $67.39   6.366%   $71.68   $71.68   $71.70   $71.70  
  7 purchase totals = $1,040.25       $1,142.5590   $1,142.55   $1,142.55   $1,142.60