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 $54.97   7.493%   $59.0889   $59.09   $59.10   $59.10  
  Purchase #2 $172.98   12.390%   $194.4122   $194.41   $194.40   $194.40  
  Purchase #3 $243.56   4.129%   $253.6166   $253.62   $253.60   $253.60  
  Purchase #4 $112.96   12.212%   $126.7547   $126.75   $126.75   $126.80  
  Purchase #5 $98.72   7.605%   $106.2277   $106.23   $106.25   $106.20  
  Purchase #6 $35.47   13.386%   $40.218   $40.22   $40.20   $40.20  
  Purchase #7 $193.43   11.692%   $216.0458   $216.05   $216.05   $216.00  
  7 purchase totals = $912.09       $996.3639   $996.37   $996.35   $996.30