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 $32.33   9.630%   $35.4434   $35.44   $35.45   $35.40  
  Purchase #2 $60.37   7.463%   $64.8754   $64.88   $64.90   $64.90  
  Purchase #3 $231.81   11.422%   $258.2873   $258.29   $258.30   $258.30  
  Purchase #4 $205.55   9.744%   $225.5788   $225.58   $225.60   $225.60  
  Purchase #5 $24.63   4.338%   $25.6984   $25.70   $25.70   $25.70  
  Purchase #6 $233.66   11.495%   $260.5192   $260.52   $260.50   $260.50  
  Purchase #7 $237.87   13.230%   $269.3402   $269.34   $269.35   $269.30  
  7 purchase totals = $1,026.22       $1,139.7427   $1,139.75   $1,139.80   $1,139.70