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 $52.93   5.317%   $55.7443   $55.74   $55.75   $55.70  
  Purchase #2 $231.74   6.797%   $247.4914   $247.49   $247.50   $247.50  
  Purchase #3 $120.77   13.580%   $137.1706   $137.17   $137.15   $137.20  
  Purchase #4 $206.41   11.794%   $230.754   $230.75   $230.75   $230.80  
  Purchase #5 $149.85   12.547%   $168.6517   $168.65   $168.65   $168.70  
  Purchase #6 $27.66   10.588%   $30.5886   $30.59   $30.60   $30.60  
  Purchase #7 $90.68   5.633%   $95.788   $95.79   $95.80   $95.80  
  7 purchase totals = $880.04       $966.1886   $966.18   $966.20   $966.30