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 $233.51   7.471%   $250.9555   $250.96   $250.95   $251.00  
  Purchase #2 $211.62   6.570%   $225.5234   $225.52   $225.50   $225.50  
  Purchase #3 $70.99   4.865%   $74.4437   $74.44   $74.45   $74.40  
  Purchase #4 $156.54   10.365%   $172.7654   $172.77   $172.75   $172.80  
  Purchase #5 $196.86   5.594%   $207.8723   $207.87   $207.85   $207.90  
  Purchase #6 $107.98   13.837%   $122.9212   $122.92   $122.90   $122.90  
  Purchase #7 $241.77   7.735%   $260.4709   $260.47   $260.45   $260.50  
  7 purchase totals = $1,219.27       $1,314.9524   $1,314.95   $1,314.85   $1,315.00