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 $77.51   11.222%   $86.2082   $86.21   $86.20   $86.20  
  Purchase #2 $59.36   5.558%   $62.6592   $62.66   $62.65   $62.70  
  Purchase #3 $242.84   8.797%   $264.2026   $264.20   $264.20   $264.20  
  Purchase #4 $61.30   10.454%   $67.7083   $67.71   $67.70   $67.70  
  Purchase #5 $64.66   7.700%   $69.6388   $69.64   $69.65   $69.60  
  Purchase #6 $56.92   11.386%   $63.4009   $63.40   $63.40   $63.40  
  Purchase #7 $177.64   6.630%   $189.4175   $189.42   $189.40   $189.40  
  7 purchase totals = $740.23       $803.2355   $803.24   $803.20   $803.20