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 $188.65   8.476%   $204.64   $204.64   $204.65   $204.60  
  Purchase #2 $114.66   3.558%   $118.7396   $118.74   $118.75   $118.70  
  Purchase #3 $27.95   4.201%   $29.1242   $29.12   $29.10   $29.10  
  Purchase #4 $234.79   13.861%   $267.3342   $267.33   $267.35   $267.30  
  Purchase #5 $202.63   7.677%   $218.1859   $218.19   $218.20   $218.20  
  Purchase #6 $186.77   4.597%   $195.3558   $195.36   $195.35   $195.40  
  Purchase #7 $115.45   12.698%   $130.1098   $130.11   $130.10   $130.10  
  7 purchase totals = $1,070.90       $1,163.4895   $1,163.49   $1,163.50   $1,163.40