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 $63.74   6.723%   $68.0252   $68.03   $68.05   $68.00  
  Purchase #2 $8.53   4.292%   $8.8961   $8.90   $8.90   $8.90  
  Purchase #3 $171.66   9.852%   $188.5719   $188.57   $188.55   $188.60  
  Purchase #4 $59.25   6.290%   $62.9768   $62.98   $63.00   $63.00  
  Purchase #5 $211.84   9.623%   $232.2254   $232.23   $232.25   $232.20  
  Purchase #6 $58.46   3.500%   $60.5061   $60.51   $60.50   $60.50  
  Purchase #7 $31.61   3.747%   $32.7944   $32.79   $32.80   $32.80  
  7 purchase totals = $605.09       $653.9959   $654.01   $654.05   $654.00