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 $170.59   3.318%   $176.2502   $176.25   $176.25   $176.30  
  Purchase #2 $5.96   3.516%   $6.1696   $6.17   $6.15   $6.20  
  Purchase #3 $55.37   9.616%   $60.6944   $60.69   $60.70   $60.70  
  Purchase #4 $225.31   12.544%   $253.5729   $253.57   $253.55   $253.60  
  Purchase #5 $223.25   4.135%   $232.4814   $232.48   $232.50   $232.50  
  Purchase #6 $88.70   12.448%   $99.7414   $99.74   $99.75   $99.70  
  Purchase #7 $51.69   4.208%   $53.8651   $53.87   $53.85   $53.90  
  7 purchase totals = $820.87       $882.7750   $882.77   $882.75   $882.90