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 $152.55   10.433%   $168.4655   $168.47   $168.45   $168.50  
  Purchase #2 $92.97   3.865%   $96.5633   $96.56   $96.55   $96.60  
  Purchase #3 $66.55   6.168%   $70.6548   $70.65   $70.65   $70.70  
  Purchase #4 $92.41   3.437%   $95.5861   $95.59   $95.60   $95.60  
  Purchase #5 $238.97   5.507%   $252.1301   $252.13   $252.15   $252.10  
  Purchase #6 $122.47   7.564%   $131.7336   $131.73   $131.75   $131.70  
  Purchase #7 $88.87   4.532%   $92.8976   $92.90   $92.90   $92.90  
  7 purchase totals = $854.79       $908.0310   $908.03   $908.05   $908.10