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 $96.42   5.546%   $101.7675   $101.77   $101.75   $101.80  
  Purchase #2 $71.51   13.491%   $81.1574   $81.16   $81.15   $81.20  
  Purchase #3 $85.73   5.424%   $90.38   $90.38   $90.40   $90.40  
  Purchase #4 $183.90   10.247%   $202.7442   $202.74   $202.75   $202.70  
  Purchase #5 $217.32   11.107%   $241.4577   $241.46   $241.45   $241.50  
  Purchase #6 $222.63   11.526%   $248.2903   $248.29   $248.30   $248.30  
  Purchase #7 $120.59   3.484%   $124.7914   $124.79   $124.80   $124.80  
  7 purchase totals = $998.10       $1,090.5885   $1,090.59   $1,090.60   $1,090.70