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 $54.27   11.309%   $60.4074   $60.41   $60.40   $60.40  
  Purchase #2 $107.28   11.816%   $119.9562   $119.96   $119.95   $120.00  
  Purchase #3 $52.35   10.402%   $57.7954   $57.80   $57.80   $57.80  
  Purchase #4 $68.35   13.353%   $77.4768   $77.48   $77.50   $77.50  
  Purchase #5 $155.34   4.707%   $162.6519   $162.65   $162.65   $162.70  
  Purchase #6 $128.80   3.767%   $133.6519   $133.65   $133.65   $133.70  
  Purchase #7 $211.65   8.370%   $229.3651   $229.37   $229.35   $229.40  
  7 purchase totals = $778.04       $841.3047   $841.32   $841.30   $841.50