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 $69.59   9.419%   $76.1447   $76.14   $76.15   $76.10  
  Purchase #2 $19.68   5.336%   $20.7301   $20.73   $20.75   $20.70  
  Purchase #3 $165.44   4.782%   $173.3513   $173.35   $173.35   $173.40  
  Purchase #4 $59.49   13.148%   $67.3117   $67.31   $67.30   $67.30  
  Purchase #5 $211.57   13.242%   $239.5861   $239.59   $239.60   $239.60  
  Purchase #6 $173.55   4.556%   $181.4569   $181.46   $181.45   $181.50  
  Purchase #7 $59.47   10.573%   $65.7578   $65.76   $65.75   $65.80  
  7 purchase totals = $758.79       $824.3386   $824.34   $824.35   $824.40