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 $54.77   12.338%   $61.5275   $61.53   $61.55   $61.50  
  Purchase #2 $116.92   7.506%   $125.696   $125.70   $125.70   $125.70  
  Purchase #3 $25.54   7.500%   $27.4555   $27.46   $27.45   $27.50  
  Purchase #4 $15.50   7.467%   $16.6574   $16.66   $16.65   $16.70  
  Purchase #5 $8.59   7.580%   $9.2411   $9.24   $9.25   $9.20  
  Purchase #6 $82.50   6.204%   $87.6183   $87.62   $87.60   $87.60  
  Purchase #7 $7.68   9.466%   $8.407   $8.41   $8.40   $8.40  
  7 purchase totals = $311.50       $336.6028   $336.62   $336.60   $336.60