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 $51.35   8.738%   $55.837   $55.84   $55.85   $55.80  
  Purchase #2 $241.62   4.177%   $251.7125   $251.71   $251.70   $251.70  
  Purchase #3 $82.47   12.464%   $92.7491   $92.75   $92.75   $92.70  
  Purchase #4 $91.73   7.645%   $98.7428   $98.74   $98.75   $98.70  
  Purchase #5 $121.50   4.247%   $126.6601   $126.66   $126.65   $126.70  
  Purchase #6 $171.75   9.702%   $188.4132   $188.41   $188.40   $188.40  
  Purchase #7 $135.30   7.836%   $145.9021   $145.90   $145.90   $145.90  
  7 purchase totals = $895.72       $960.0168   $960.01   $960.00   $959.90