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 $250.40   6.768%   $267.3471   $267.35   $267.35   $267.30  
  Purchase #2 $162.96   8.521%   $176.8458   $176.85   $176.85   $176.80  
  Purchase #3 $246.46   5.194%   $259.2611   $259.26   $259.25   $259.30  
  Purchase #4 $195.46   4.552%   $204.3573   $204.36   $204.35   $204.40  
  Purchase #5 $170.84   4.454%   $178.4492   $178.45   $178.45   $178.40  
  Purchase #6 $90.65   4.227%   $94.4818   $94.48   $94.50   $94.50  
  Purchase #7 $241.32   3.870%   $250.6591   $250.66   $250.65   $250.70  
  7 purchase totals = $1,358.09       $1,431.4014   $1,431.41   $1,431.40   $1,431.40