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 $13.56   12.429%   $15.2454   $15.25   $15.25   $15.20  
  Purchase #2 $249.56   11.394%   $277.9949   $277.99   $278.00   $278.00  
  Purchase #3 $86.95   3.782%   $90.2384   $90.24   $90.25   $90.20  
  Purchase #4 $196.97   3.449%   $203.7635   $203.76   $203.75   $203.80  
  Purchase #5 $191.96   4.520%   $200.6366   $200.64   $200.65   $200.60  
  Purchase #6 $220.80   4.554%   $230.8552   $230.86   $230.85   $230.90  
  Purchase #7 $60.93   7.108%   $65.2609   $65.26   $65.25   $65.30  
  7 purchase totals = $1,020.73       $1,083.9949   $1,084.00   $1,084.00   $1,084.00