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 $244.67   8.841%   $266.3013   $266.30   $266.30   $266.30  
  Purchase #2 $114.40   9.749%   $125.5529   $125.55   $125.55   $125.60  
  Purchase #3 $244.63   11.433%   $272.5985   $272.60   $272.60   $272.60  
  Purchase #4 $168.28   12.620%   $189.5169   $189.52   $189.50   $189.50  
  Purchase #5 $175.87   5.403%   $185.3723   $185.37   $185.35   $185.40  
  Purchase #6 $31.60   11.136%   $35.119   $35.12   $35.10   $35.10  
  Purchase #7 $172.36   4.482%   $180.0852   $180.09   $180.10   $180.10  
  7 purchase totals = $1,151.81       $1,254.5461   $1,254.55   $1,254.50   $1,254.60