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 $93.90   3.117%   $96.8269   $96.83   $96.85   $96.80  
  Purchase #2 $107.64   7.477%   $115.6882   $115.69   $115.70   $115.70  
  Purchase #3 $231.94   9.197%   $253.2715   $253.27   $253.25   $253.30  
  Purchase #4 $182.65   6.326%   $194.2044   $194.20   $194.20   $194.20  
  Purchase #5 $165.79   10.737%   $183.5909   $183.59   $183.60   $183.60  
  Purchase #6 $232.65   11.420%   $259.2186   $259.22   $259.20   $259.20  
  Purchase #7 $49.65   4.564%   $51.916   $51.92   $51.90   $51.90  
  7 purchase totals = $1,064.22       $1,154.7165   $1,154.72   $1,154.70   $1,154.70