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 $74.75   3.309%   $77.2235   $77.22   $77.20   $77.20  
  Purchase #2 $203.85   10.114%   $224.4674   $224.47   $224.45   $224.50  
  Purchase #3 $244.58   11.441%   $272.5624   $272.56   $272.55   $272.60  
  Purchase #4 $170.49   8.647%   $185.2323   $185.23   $185.25   $185.20  
  Purchase #5 $118.32   12.118%   $132.658   $132.66   $132.65   $132.70  
  Purchase #6 $26.34   8.777%   $28.6519   $28.65   $28.65   $28.70  
  Purchase #7 $36.80   3.548%   $38.1057   $38.11   $38.10   $38.10  
  7 purchase totals = $875.13       $958.9012   $958.90   $958.85   $959.00