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 $38.78   11.494%   $43.2374   $43.24   $43.25   $43.20  
  Purchase #2 $57.38   4.156%   $59.7647   $59.76   $59.75   $59.80  
  Purchase #3 $44.62   10.861%   $49.4662   $49.47   $49.45   $49.50  
  Purchase #4 $235.26   5.175%   $247.4347   $247.43   $247.45   $247.40  
  Purchase #5 $219.59   9.772%   $241.0483   $241.05   $241.05   $241.00  
  Purchase #6 $122.44   3.345%   $126.5356   $126.54   $126.55   $126.50  
  Purchase #7 $216.39   12.416%   $243.257   $243.26   $243.25   $243.30  
  7 purchase totals = $934.46       $1,010.7439   $1,010.75   $1,010.75   $1,010.70