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 $48.66   11.373%   $54.1941   $54.19   $54.20   $54.20  
  Purchase #2 $32.69   3.480%   $33.8276   $33.83   $33.85   $33.80  
  Purchase #3 $174.64   10.294%   $192.6174   $192.62   $192.60   $192.60  
  Purchase #4 $70.60   7.105%   $75.6161   $75.62   $75.60   $75.60  
  Purchase #5 $54.67   6.572%   $58.2629   $58.26   $58.25   $58.30  
  Purchase #6 $172.39   11.757%   $192.6579   $192.66   $192.65   $192.70  
  Purchase #7 $87.87   8.365%   $95.2203   $95.22   $95.20   $95.20  
  7 purchase totals = $641.52       $702.3963   $702.40   $702.35   $702.40