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 $122.89   8.172%   $132.9326   $132.93   $132.95   $132.90  
  Purchase #2 $53.67   12.311%   $60.2773   $60.28   $60.30   $60.30  
  Purchase #3 $30.26   7.814%   $32.6245   $32.62   $32.60   $32.60  
  Purchase #4 $116.95   11.727%   $130.6647   $130.66   $130.65   $130.70  
  Purchase #5 $223.93   8.559%   $243.0962   $243.10   $243.10   $243.10  
  Purchase #6 $220.83   13.834%   $251.3796   $251.38   $251.40   $251.40  
  Purchase #7 $226.47   8.562%   $245.8604   $245.86   $245.85   $245.90  
  7 purchase totals = $995.00       $1,096.8353   $1,096.83   $1,096.85   $1,096.90