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 $218.48   12.288%   $245.3268   $245.33   $245.35   $245.30  
  Purchase #2 $88.73   9.617%   $97.2632   $97.26   $97.25   $97.30  
  Purchase #3 $136.76   8.213%   $147.9921   $147.99   $148.00   $148.00  
  Purchase #4 $214.66   8.590%   $233.0993   $233.10   $233.10   $233.10  
  Purchase #5 $238.89   10.353%   $263.6223   $263.62   $263.60   $263.60  
  Purchase #6 $41.79   11.517%   $46.603   $46.60   $46.60   $46.60  
  Purchase #7 $62.69   3.432%   $64.8415   $64.84   $64.85   $64.80  
  7 purchase totals = $1,002.00       $1,098.7482   $1,098.74   $1,098.75   $1,098.70