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 $247.61   7.526%   $266.2451   $266.25   $266.25   $266.20  
  Purchase #2 $80.93   9.575%   $88.679   $88.68   $88.70   $88.70  
  Purchase #3 $11.81   3.867%   $12.2667   $12.27   $12.25   $12.30  
  Purchase #4 $118.26   4.142%   $123.1583   $123.16   $123.15   $123.20  
  Purchase #5 $176.27   6.276%   $187.3327   $187.33   $187.35   $187.30  
  Purchase #6 $232.29   3.739%   $240.9753   $240.98   $241.00   $241.00  
  Purchase #7 $40.97   13.833%   $46.6374   $46.64   $46.65   $46.60  
  7 purchase totals = $908.14       $965.2945   $965.31   $965.35   $965.30