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 $55.39   6.534%   $59.0092   $59.01   $59.00   $59.00  
  Purchase #2 $200.92   3.357%   $207.6649   $207.66   $207.65   $207.70  
  Purchase #3 $243.73   8.393%   $264.1863   $264.19   $264.20   $264.20  
  Purchase #4 $161.53   7.871%   $174.244   $174.24   $174.25   $174.20  
  Purchase #5 $19.39   11.256%   $21.5725   $21.57   $21.55   $21.60  
  Purchase #6 $20.70   8.248%   $22.4073   $22.41   $22.40   $22.40  
  Purchase #7 $32.58   10.264%   $35.924   $35.92   $35.90   $35.90  
  7 purchase totals = $734.24       $785.0082   $785.00   $784.95   $785.00