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 $232.52   11.648%   $259.6039   $259.60   $259.60   $259.60  
  Purchase #2 $29.28   13.381%   $33.198   $33.20   $33.20   $33.20  
  Purchase #3 $133.41   8.151%   $144.2842   $144.28   $144.30   $144.30  
  Purchase #4 $94.28   8.162%   $101.9751   $101.98   $102.00   $102.00  
  Purchase #5 $192.40   6.753%   $205.3928   $205.39   $205.40   $205.40  
  Purchase #6 $244.32   3.867%   $253.7679   $253.77   $253.75   $253.80  
  Purchase #7 $240.54   10.680%   $266.2297   $266.23   $266.25   $266.20  
  7 purchase totals = $1,166.75       $1,264.4516   $1,264.45   $1,264.50   $1,264.50