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 $250.53   6.824%   $267.6262   $267.63   $267.65   $267.60  
  Purchase #2 $160.71   7.853%   $173.3306   $173.33   $173.35   $173.30  
  Purchase #3 $225.83   4.365%   $235.6875   $235.69   $235.70   $235.70  
  Purchase #4 $88.82   6.533%   $94.6226   $94.62   $94.60   $94.60  
  Purchase #5 $113.96   4.771%   $119.397   $119.40   $119.40   $119.40  
  Purchase #6 $6.37   9.512%   $6.9759   $6.98   $7.00   $7.00  
  Purchase #7 $183.80   11.488%   $204.9149   $204.91   $204.90   $204.90  
  7 purchase totals = $1,030.02       $1,102.5547   $1,102.56   $1,102.60   $1,102.50