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 $178.63   11.787%   $199.6851   $199.69   $199.70   $199.70  
  Purchase #2 $166.97   10.742%   $184.9059   $184.91   $184.90   $184.90  
  Purchase #3 $49.82   11.517%   $55.5578   $55.56   $55.55   $55.60  
  Purchase #4 $175.96   5.416%   $185.49   $185.49   $185.50   $185.50  
  Purchase #5 $242.69   11.107%   $269.6456   $269.65   $269.65   $269.60  
  Purchase #6 $172.79   12.427%   $194.2626   $194.26   $194.25   $194.30  
  Purchase #7 $24.62   6.108%   $26.1238   $26.12   $26.10   $26.10  
  7 purchase totals = $1,011.48       $1,115.6708   $1,115.68   $1,115.65   $1,115.70