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 $120.71   8.751%   $131.2733   $131.27   $131.25   $131.30  
  Purchase #2 $233.78   5.795%   $247.3276   $247.33   $247.35   $247.30  
  Purchase #3 $109.47   5.842%   $115.8652   $115.87   $115.85   $115.90  
  Purchase #4 $226.61   8.200%   $245.192   $245.19   $245.20   $245.20  
  Purchase #5 $73.45   6.261%   $78.0487   $78.05   $78.05   $78.00  
  Purchase #6 $16.98   5.430%   $17.902   $17.90   $17.90   $17.90  
  Purchase #7 $44.89   10.841%   $49.7565   $49.76   $49.75   $49.80  
  7 purchase totals = $825.89       $885.3653   $885.37   $885.35   $885.40