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 $81.53   12.816%   $91.9789   $91.98   $92.00   $92.00  
  Purchase #2 $220.94   6.825%   $236.0192   $236.02   $236.00   $236.00  
  Purchase #3 $250.99   13.450%   $284.7482   $284.75   $284.75   $284.70  
  Purchase #4 $168.84   11.636%   $188.4862   $188.49   $188.50   $188.50  
  Purchase #5 $118.51   7.133%   $126.9633   $126.96   $126.95   $127.00  
  Purchase #6 $233.82   10.517%   $258.4108   $258.41   $258.40   $258.40  
  Purchase #7 $84.81   3.862%   $88.0854   $88.09   $88.10   $88.10  
  7 purchase totals = $1,159.44       $1,274.6920   $1,274.70   $1,274.70   $1,274.70