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 $238.61   8.379%   $258.6031   $258.60   $258.60   $258.60  
  Purchase #2 $119.75   4.798%   $125.4956   $125.50   $125.50   $125.50  
  Purchase #3 $207.70   8.527%   $225.4106   $225.41   $225.40   $225.40  
  Purchase #4 $120.52   4.425%   $125.853   $125.85   $125.85   $125.90  
  Purchase #5 $135.80   4.388%   $141.7589   $141.76   $141.75   $141.80  
  Purchase #6 $13.99   8.594%   $15.1923   $15.19   $15.20   $15.20  
  Purchase #7 $181.40   12.569%   $204.2002   $204.20   $204.20   $204.20  
  7 purchase totals = $1,017.77       $1,096.5137   $1,096.51   $1,096.50   $1,096.60