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 $239.94   9.337%   $262.3432   $262.34   $262.35   $262.30  
  Purchase #2 $218.30   4.419%   $227.9467   $227.95   $227.95   $227.90  
  Purchase #3 $195.94   11.464%   $218.4026   $218.40   $218.40   $218.40  
  Purchase #4 $60.59   6.108%   $64.2908   $64.29   $64.30   $64.30  
  Purchase #5 $188.93   11.689%   $211.014   $211.01   $211.00   $211.00  
  Purchase #6 $209.34   9.128%   $228.4486   $228.45   $228.45   $228.40  
  Purchase #7 $243.25   11.119%   $270.297   $270.30   $270.30   $270.30  
  7 purchase totals = $1,356.29       $1,482.7429   $1,482.74   $1,482.75   $1,482.60