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 $36.89   12.173%   $41.3806   $41.38   $41.40   $41.40  
  Purchase #2 $172.46   8.425%   $186.9898   $186.99   $187.00   $187.00  
  Purchase #3 $58.38   9.634%   $64.0043   $64.00   $64.00   $64.00  
  Purchase #4 $151.65   3.500%   $156.9578   $156.96   $156.95   $157.00  
  Purchase #5 $188.48   13.111%   $213.1916   $213.19   $213.20   $213.20  
  Purchase #6 $193.67   12.781%   $218.423   $218.42   $218.40   $218.40  
  Purchase #7 $120.60   5.142%   $126.8013   $126.80   $126.80   $126.80  
  7 purchase totals = $922.13       $1,007.7484   $1,007.74   $1,007.75   $1,007.80