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 $46.94   10.136%   $51.6978   $51.70   $51.70   $51.70  
  Purchase #2 $191.91   11.249%   $213.498   $213.50   $213.50   $213.50  
  Purchase #3 $131.73   4.822%   $138.082   $138.08   $138.10   $138.10  
  Purchase #4 $68.29   9.111%   $74.5119   $74.51   $74.50   $74.50  
  Purchase #5 $245.78   8.283%   $266.138   $266.14   $266.15   $266.10  
  Purchase #6 $199.94   11.626%   $223.185   $223.19   $223.20   $223.20  
  Purchase #7 $214.74   3.194%   $221.5988   $221.60   $221.60   $221.60  
  7 purchase totals = $1,099.33       $1,188.7115   $1,188.72   $1,188.75   $1,188.70