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 $242.27   10.310%   $267.248   $267.25   $267.25   $267.20  
  Purchase #2 $35.47   10.210%   $39.0915   $39.09   $39.10   $39.10  
  Purchase #3 $125.60   4.260%   $130.9506   $130.95   $130.95   $131.00  
  Purchase #4 $138.28   10.669%   $153.0331   $153.03   $153.05   $153.00  
  Purchase #5 $189.66   6.719%   $202.4033   $202.40   $202.40   $202.40  
  Purchase #6 $79.74   10.440%   $88.0649   $88.06   $88.05   $88.10  
  Purchase #7 $174.63   10.411%   $192.8107   $192.81   $192.80   $192.80  
  7 purchase totals = $985.65       $1,073.6021   $1,073.59   $1,073.60   $1,073.60