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 $208.51   7.793%   $224.7592   $224.76   $224.75   $224.80  
  Purchase #2 $203.81   6.146%   $216.3362   $216.34   $216.35   $216.30  
  Purchase #3 $245.97   5.740%   $260.0887   $260.09   $260.10   $260.10  
  Purchase #4 $231.55   3.589%   $239.8603   $239.86   $239.85   $239.90  
  Purchase #5 $185.64   4.812%   $194.573   $194.57   $194.55   $194.60  
  Purchase #6 $164.71   11.577%   $183.7785   $183.78   $183.80   $183.80  
  Purchase #7 $202.34   5.121%   $212.7018   $212.70   $212.70   $212.70  
  7 purchase totals = $1,442.53       $1,532.0977   $1,532.10   $1,532.10   $1,532.20