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 $104.37   4.577%   $109.147   $109.15   $109.15   $109.10  
  Purchase #2 $244.99   9.782%   $268.9549   $268.95   $268.95   $269.00  
  Purchase #3 $218.52   8.635%   $237.3892   $237.39   $237.40   $237.40  
  Purchase #4 $204.97   6.719%   $218.7419   $218.74   $218.75   $218.70  
  Purchase #5 $87.50   8.616%   $95.039   $95.04   $95.05   $95.00  
  Purchase #6 $168.45   5.581%   $177.8512   $177.85   $177.85   $177.90  
  Purchase #7 $239.84   7.831%   $258.6219   $258.62   $258.60   $258.60  
  7 purchase totals = $1,268.64       $1,365.7451   $1,365.74   $1,365.75   $1,365.70