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 $159.83   10.461%   $176.5498   $176.55   $176.55   $176.50  
  Purchase #2 $189.79   11.297%   $211.2306   $211.23   $211.25   $211.20  
  Purchase #3 $67.45   13.784%   $76.7473   $76.75   $76.75   $76.70  
  Purchase #4 $6.96   9.143%   $7.5964   $7.60   $7.60   $7.60  
  Purchase #5 $53.77   4.791%   $56.3461   $56.35   $56.35   $56.30  
  Purchase #6 $219.45   13.111%   $248.2221   $248.22   $248.20   $248.20  
  Purchase #7 $154.46   12.333%   $173.5096   $173.51   $173.50   $173.50  
  7 purchase totals = $851.71       $950.2019   $950.21   $950.20   $950.00