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 $184.87   6.205%   $196.3412   $196.34   $196.35   $196.30  
  Purchase #2 $167.30   13.204%   $189.3903   $189.39   $189.40   $189.40  
  Purchase #3 $9.97   6.403%   $10.6084   $10.61   $10.60   $10.60  
  Purchase #4 $228.83   10.874%   $253.713   $253.71   $253.70   $253.70  
  Purchase #5 $162.79   6.647%   $173.6107   $173.61   $173.60   $173.60  
  Purchase #6 $228.65   6.822%   $244.2485   $244.25   $244.25   $244.20  
  Purchase #7 $14.45   9.118%   $15.7676   $15.77   $15.75   $15.80  
  7 purchase totals = $996.86       $1,083.6797   $1,083.68   $1,083.65   $1,083.60