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 $66.51   8.784%   $72.3522   $72.35   $72.35   $72.40  
  Purchase #2 $62.67   13.376%   $71.0527   $71.05   $71.05   $71.10  
  Purchase #3 $34.84   6.172%   $36.9903   $36.99   $37.00   $37.00  
  Purchase #4 $72.62   6.422%   $77.2837   $77.28   $77.30   $77.30  
  Purchase #5 $229.99   9.275%   $251.3216   $251.32   $251.30   $251.30  
  Purchase #6 $241.25   11.347%   $268.6246   $268.62   $268.60   $268.60  
  Purchase #7 $70.55   8.332%   $76.4282   $76.43   $76.45   $76.40  
  7 purchase totals = $778.43       $854.0533   $854.04   $854.05   $854.10