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 $126.57   7.587%   $136.1729   $136.17   $136.15   $136.20  
  Purchase #2 $110.71   11.644%   $123.6011   $123.60   $123.60   $123.60  
  Purchase #3 $95.45   13.549%   $108.3825   $108.38   $108.40   $108.40  
  Purchase #4 $147.41   4.383%   $153.871   $153.87   $153.85   $153.90  
  Purchase #5 $196.84   10.311%   $217.1362   $217.14   $217.15   $217.10  
  Purchase #6 $167.31   11.825%   $187.0944   $187.09   $187.10   $187.10  
  Purchase #7 $68.93   8.827%   $75.0145   $75.01   $75.00   $75.00  
  7 purchase totals = $913.22       $1,001.2726   $1,001.26   $1,001.25   $1,001.30