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 $110.69   11.214%   $123.1028   $123.10   $123.10   $123.10  
  Purchase #2 $183.80   13.832%   $209.2232   $209.22   $209.20   $209.20  
  Purchase #3 $55.71   7.247%   $59.7473   $59.75   $59.75   $59.70  
  Purchase #4 $103.56   7.394%   $111.2172   $111.22   $111.20   $111.20  
  Purchase #5 $123.41   6.263%   $131.1392   $131.14   $131.15   $131.10  
  Purchase #6 $53.26   12.744%   $60.0475   $60.05   $60.05   $60.00  
  Purchase #7 $109.60   10.601%   $121.2187   $121.22   $121.20   $121.20  
  7 purchase totals = $740.03       $815.6959   $815.70   $815.65   $815.50