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 $42.48   12.381%   $47.7394   $47.74   $47.75   $47.70  
  Purchase #2 $200.95   5.503%   $212.0083   $212.01   $212.00   $212.00  
  Purchase #3 $213.68   7.854%   $230.4624   $230.46   $230.45   $230.50  
  Purchase #4 $195.98   10.498%   $216.554   $216.55   $216.55   $216.60  
  Purchase #5 $85.33   12.564%   $96.0509   $96.05   $96.05   $96.10  
  Purchase #6 $68.51   13.373%   $77.6718   $77.67   $77.65   $77.70  
  Purchase #7 $76.57   10.449%   $84.5708   $84.57   $84.55   $84.60  
  7 purchase totals = $883.50       $965.0576   $965.05   $965.00   $965.20