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 $70.62   9.796%   $77.5379   $77.54   $77.55   $77.50  
  Purchase #2 $23.53   9.271%   $25.7115   $25.71   $25.70   $25.70  
  Purchase #3 $67.66   11.279%   $75.2914   $75.29   $75.30   $75.30  
  Purchase #4 $203.68   5.113%   $214.0942   $214.09   $214.10   $214.10  
  Purchase #5 $187.99   13.864%   $214.0529   $214.05   $214.05   $214.10  
  Purchase #6 $12.33   12.694%   $13.8952   $13.90   $13.90   $13.90  
  Purchase #7 $225.92   3.126%   $232.9823   $232.98   $233.00   $233.00  
  7 purchase totals = $791.73       $853.5654   $853.56   $853.60   $853.60