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 $193.60   11.801%   $216.4467   $216.45   $216.45   $216.40  
  Purchase #2 $85.98   11.869%   $96.185   $96.19   $96.20   $96.20  
  Purchase #3 $56.98   11.721%   $63.6586   $63.66   $63.65   $63.70  
  Purchase #4 $206.61   10.590%   $228.49   $228.49   $228.50   $228.50  
  Purchase #5 $72.31   7.165%   $77.491   $77.49   $77.50   $77.50  
  Purchase #6 $85.32   13.557%   $96.8868   $96.89   $96.90   $96.90  
  Purchase #7 $8.35   13.206%   $9.4527   $9.45   $9.45   $9.50  
  7 purchase totals = $709.15       $788.6108   $788.62   $788.65   $788.70