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 $85.34   13.313%   $96.7013   $96.70   $96.70   $96.70  
  Purchase #2 $45.84   8.873%   $49.9074   $49.91   $49.90   $49.90  
  Purchase #3 $114.94   9.146%   $125.4524   $125.45   $125.45   $125.50  
  Purchase #4 $250.25   8.234%   $270.8556   $270.86   $270.85   $270.90  
  Purchase #5 $194.73   9.678%   $213.576   $213.58   $213.60   $213.60  
  Purchase #6 $100.96   5.389%   $106.4007   $106.40   $106.40   $106.40  
  Purchase #7 $196.33   6.495%   $209.0816   $209.08   $209.10   $209.10  
  7 purchase totals = $988.39       $1,071.9750   $1,071.98   $1,072.00   $1,072.10