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 $44.87   5.323%   $47.2584   $47.26   $47.25   $47.30  
  Purchase #2 $189.95   8.362%   $205.8336   $205.83   $205.85   $205.80  
  Purchase #3 $127.85   5.275%   $134.5941   $134.59   $134.60   $134.60  
  Purchase #4 $175.73   5.566%   $185.5111   $185.51   $185.50   $185.50  
  Purchase #5 $115.47   11.661%   $128.935   $128.94   $128.95   $128.90  
  Purchase #6 $14.58   8.373%   $15.8008   $15.80   $15.80   $15.80  
  Purchase #7 $37.69   5.213%   $39.6548   $39.65   $39.65   $39.70  
  7 purchase totals = $706.14       $757.5878   $757.58   $757.60   $757.60