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 $57.45   5.582%   $60.6569   $60.66   $60.65   $60.70  
  Purchase #2 $8.38   4.779%   $8.7805   $8.78   $8.80   $8.80  
  Purchase #3 $120.74   4.476%   $126.1443   $126.14   $126.15   $126.10  
  Purchase #4 $245.61   6.507%   $261.5918   $261.59   $261.60   $261.60  
  Purchase #5 $220.68   8.484%   $239.4025   $239.40   $239.40   $239.40  
  Purchase #6 $70.49   9.722%   $77.343   $77.34   $77.35   $77.30  
  Purchase #7 $9.51   5.793%   $10.0609   $10.06   $10.05   $10.10  
  7 purchase totals = $732.86       $783.9799   $783.97   $784.00   $784.00