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 $58.54   3.339%   $60.4947   $60.49   $60.50   $60.50  
  Purchase #2 $82.83   10.562%   $91.5785   $91.58   $91.60   $91.60  
  Purchase #3 $131.40   12.715%   $148.1075   $148.11   $148.10   $148.10  
  Purchase #4 $199.97   13.420%   $226.806   $226.81   $226.80   $226.80  
  Purchase #5 $139.82   10.833%   $154.9667   $154.97   $154.95   $155.00  
  Purchase #6 $244.29   7.592%   $262.8365   $262.84   $262.85   $262.80  
  Purchase #7 $99.25   5.352%   $104.5619   $104.56   $104.55   $104.60  
  7 purchase totals = $956.10       $1,049.3518   $1,049.36   $1,049.35   $1,049.40