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 $223.40   3.234%   $230.6248   $230.62   $230.60   $230.60  
  Purchase #2 $224.58   11.439%   $250.2697   $250.27   $250.25   $250.30  
  Purchase #3 $96.44   12.443%   $108.44   $108.44   $108.45   $108.40  
  Purchase #4 $228.68   13.477%   $259.4992   $259.50   $259.50   $259.50  
  Purchase #5 $153.39   7.464%   $164.839   $164.84   $164.85   $164.80  
  Purchase #6 $40.45   12.684%   $45.5807   $45.58   $45.60   $45.60  
  Purchase #7 $227.52   7.366%   $244.2791   $244.28   $244.30   $244.30  
  7 purchase totals = $1,194.46       $1,303.5325   $1,303.53   $1,303.55   $1,303.50