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 $69.66   6.573%   $74.2388   $74.24   $74.25   $74.20  
  Purchase #2 $80.73   6.520%   $85.9936   $85.99   $86.00   $86.00  
  Purchase #3 $8.59   9.476%   $9.404   $9.40   $9.40   $9.40  
  Purchase #4 $86.27   7.308%   $92.5746   $92.57   $92.55   $92.60  
  Purchase #5 $201.53   9.570%   $220.8164   $220.82   $220.80   $220.80  
  Purchase #6 $106.64   4.564%   $111.507   $111.51   $111.50   $111.50  
  Purchase #7 $54.94   6.478%   $58.499   $58.50   $58.50   $58.50  
  7 purchase totals = $608.36       $653.0334   $653.03   $653.00   $653.00