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 $22.43   3.638%   $23.246   $23.25   $23.25   $23.20  
  Purchase #2 $106.98   4.305%   $111.5855   $111.59   $111.60   $111.60  
  Purchase #3 $200.32   12.148%   $224.6549   $224.65   $224.65   $224.70  
  Purchase #4 $223.41   7.108%   $239.29   $239.29   $239.30   $239.30  
  Purchase #5 $74.71   6.785%   $79.7791   $79.78   $79.80   $79.80  
  Purchase #6 $202.65   6.407%   $215.6338   $215.63   $215.65   $215.60  
  Purchase #7 $128.97   8.435%   $139.8486   $139.85   $139.85   $139.80  
  7 purchase totals = $959.47       $1,034.0379   $1,034.04   $1,034.10   $1,034.00