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 $225.56   4.145%   $234.9095   $234.91   $234.90   $234.90  
  Purchase #2 $184.88   4.327%   $192.8798   $192.88   $192.90   $192.90  
  Purchase #3 $46.74   5.215%   $49.1775   $49.18   $49.20   $49.20  
  Purchase #4 $244.94   11.150%   $272.2508   $272.25   $272.25   $272.30  
  Purchase #5 $151.56   12.851%   $171.037   $171.04   $171.05   $171.00  
  Purchase #6 $231.27   5.773%   $244.6212   $244.62   $244.60   $244.60  
  Purchase #7 $23.85   11.632%   $26.6242   $26.62   $26.60   $26.60  
  7 purchase totals = $1,108.80       $1,191.5000   $1,191.50   $1,191.50   $1,191.50