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 $244.36   7.501%   $262.6894   $262.69   $262.70   $262.70  
  Purchase #2 $23.65   3.796%   $24.5478   $24.55   $24.55   $24.50  
  Purchase #3 $44.31   4.428%   $46.272   $46.27   $46.25   $46.30  
  Purchase #4 $153.75   11.136%   $170.8716   $170.87   $170.85   $170.90  
  Purchase #5 $178.80   13.751%   $203.3868   $203.39   $203.40   $203.40  
  Purchase #6 $58.29   12.674%   $65.6777   $65.68   $65.70   $65.70  
  Purchase #7 $155.58   4.785%   $163.0245   $163.02   $163.00   $163.00  
  7 purchase totals = $858.74       $936.4698   $936.47   $936.45   $936.50