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 $167.78   10.151%   $184.8113   $184.81   $184.80   $184.80  
  Purchase #2 $168.48   11.151%   $187.2672   $187.27   $187.25   $187.30  
  Purchase #3 $230.44   3.401%   $238.2773   $238.28   $238.30   $238.30  
  Purchase #4 $125.38   13.412%   $142.196   $142.20   $142.20   $142.20  
  Purchase #5 $174.32   9.586%   $191.0303   $191.03   $191.05   $191.00  
  Purchase #6 $43.39   10.530%   $47.959   $47.96   $47.95   $48.00  
  Purchase #7 $21.26   8.239%   $23.0116   $23.01   $23.00   $23.00  
  7 purchase totals = $931.05       $1,014.5527   $1,014.56   $1,014.55   $1,014.60