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 $211.37   11.634%   $235.9608   $235.96   $235.95   $236.00  
  Purchase #2 $160.72   12.779%   $181.2584   $181.26   $181.25   $181.30  
  Purchase #3 $200.54   8.298%   $217.1808   $217.18   $217.20   $217.20  
  Purchase #4 $41.54   9.694%   $45.5669   $45.57   $45.55   $45.60  
  Purchase #5 $213.63   6.247%   $226.9755   $226.98   $227.00   $227.00  
  Purchase #6 $248.95   4.616%   $260.4415   $260.44   $260.45   $260.40  
  Purchase #7 $37.59   10.709%   $41.6155   $41.62   $41.60   $41.60  
  7 purchase totals = $1,114.34       $1,208.9994   $1,209.01   $1,209.00   $1,209.10