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 $54.97   11.498%   $61.2905   $61.29   $61.30   $61.30  
  Purchase #2 $234.41   8.235%   $253.7137   $253.71   $253.70   $253.70  
  Purchase #3 $95.49   9.126%   $104.2044   $104.20   $104.20   $104.20  
  Purchase #4 $201.94   8.854%   $219.8198   $219.82   $219.80   $219.80  
  Purchase #5 $118.54   6.697%   $126.4786   $126.48   $126.50   $126.50  
  Purchase #6 $108.41   6.844%   $115.8296   $115.83   $115.85   $115.80  
  Purchase #7 $179.37   10.187%   $197.6424   $197.64   $197.65   $197.60  
  7 purchase totals = $993.13       $1,078.9790   $1,078.97   $1,079.00   $1,078.90