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 $65.26   5.481%   $68.8369   $68.84   $68.85   $68.80  
  Purchase #2 $145.61   12.394%   $163.6569   $163.66   $163.65   $163.70  
  Purchase #3 $100.66   8.576%   $109.2926   $109.29   $109.30   $109.30  
  Purchase #4 $163.61   7.544%   $175.9527   $175.95   $175.95   $176.00  
  Purchase #5 $127.41   8.777%   $138.5928   $138.59   $138.60   $138.60  
  Purchase #6 $181.50   12.808%   $204.7465   $204.75   $204.75   $204.70  
  Purchase #7 $125.85   3.354%   $130.071   $130.07   $130.05   $130.10  
  7 purchase totals = $909.90       $991.1494   $991.15   $991.15   $991.20