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 $184.81   7.590%   $198.8371   $198.84   $198.85   $198.80  
  Purchase #2 $157.45   4.568%   $164.6423   $164.64   $164.65   $164.60  
  Purchase #3 $48.89   4.285%   $50.9849   $50.98   $51.00   $51.00  
  Purchase #4 $62.29   12.237%   $69.9124   $69.91   $69.90   $69.90  
  Purchase #5 $173.89   13.452%   $197.2817   $197.28   $197.30   $197.30  
  Purchase #6 $126.79   3.757%   $131.5535   $131.55   $131.55   $131.60  
  Purchase #7 $234.96   6.407%   $250.0139   $250.01   $250.00   $250.00  
  7 purchase totals = $989.08       $1,063.2258   $1,063.21   $1,063.25   $1,063.20