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 $199.44   6.202%   $211.8093   $211.81   $211.80   $211.80  
  Purchase #2 $68.37   7.785%   $73.6926   $73.69   $73.70   $73.70  
  Purchase #3 $148.40   11.424%   $165.3532   $165.35   $165.35   $165.40  
  Purchase #4 $56.93   10.292%   $62.7892   $62.79   $62.80   $62.80  
  Purchase #5 $161.78   10.622%   $178.9643   $178.96   $178.95   $179.00  
  Purchase #6 $183.62   8.698%   $199.5913   $199.59   $199.60   $199.60  
  Purchase #7 $144.43   12.834%   $162.9661   $162.97   $162.95   $163.00  
  7 purchase totals = $962.97       $1,055.1660   $1,055.16   $1,055.15   $1,055.30