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 $187.88   10.234%   $207.1076   $207.11   $207.10   $207.10  
  Purchase #2 $102.58   8.143%   $110.9331   $110.93   $110.95   $110.90  
  Purchase #3 $106.33   7.457%   $114.259   $114.26   $114.25   $114.30  
  Purchase #4 $43.31   13.251%   $49.049   $49.05   $49.05   $49.00  
  Purchase #5 $118.38   4.675%   $123.9143   $123.91   $123.90   $123.90  
  Purchase #6 $178.29   7.425%   $191.528   $191.53   $191.55   $191.50  
  Purchase #7 $224.61   9.865%   $246.7678   $246.77   $246.75   $246.80  
  7 purchase totals = $961.38       $1,043.5588   $1,043.56   $1,043.55   $1,043.50