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 $163.59   11.762%   $182.8315   $182.83   $182.85   $182.80  
  Purchase #2 $50.87   9.154%   $55.5266   $55.53   $55.55   $55.50  
  Purchase #3 $171.79   12.364%   $193.0301   $193.03   $193.05   $193.00  
  Purchase #4 $52.87   7.356%   $56.7591   $56.76   $56.75   $56.80  
  Purchase #5 $81.51   12.623%   $91.799   $91.80   $91.80   $91.80  
  Purchase #6 $200.70   8.756%   $218.2733   $218.27   $218.25   $218.30  
  Purchase #7 $136.56   10.297%   $150.6216   $150.62   $150.60   $150.60  
  7 purchase totals = $857.89       $948.8412   $948.84   $948.85   $948.80