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 $183.90   12.568%   $207.0126   $207.01   $207.00   $207.00  
  Purchase #2 $190.62   4.225%   $198.6737   $198.67   $198.65   $198.70  
  Purchase #3 $53.44   5.127%   $56.1799   $56.18   $56.20   $56.20  
  Purchase #4 $217.56   9.537%   $238.3087   $238.31   $238.30   $238.30  
  Purchase #5 $117.72   13.567%   $133.6911   $133.69   $133.70   $133.70  
  Purchase #6 $180.53   4.606%   $188.8452   $188.85   $188.85   $188.80  
  Purchase #7 $155.84   12.222%   $174.8868   $174.89   $174.90   $174.90  
  7 purchase totals = $1,099.61       $1,197.5980   $1,197.60   $1,197.60   $1,197.60