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 $227.81   13.584%   $258.7557   $258.76   $258.75   $258.80  
  Purchase #2 $187.67   9.242%   $205.0145   $205.01   $205.00   $205.00  
  Purchase #3 $59.66   5.774%   $63.1048   $63.10   $63.10   $63.10  
  Purchase #4 $240.60   8.188%   $260.3003   $260.30   $260.30   $260.30  
  Purchase #5 $193.70   5.649%   $204.6421   $204.64   $204.65   $204.60  
  Purchase #6 $178.84   3.336%   $184.8061   $184.81   $184.80   $184.80  
  Purchase #7 $118.87   10.587%   $131.4548   $131.45   $131.45   $131.50  
  7 purchase totals = $1,207.15       $1,308.0783   $1,308.07   $1,308.05   $1,308.10