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 $192.65   13.559%   $218.7714   $218.77   $218.75   $218.80  
  Purchase #2 $91.86   12.447%   $103.2938   $103.29   $103.30   $103.30  
  Purchase #3 $173.75   13.642%   $197.453   $197.45   $197.45   $197.50  
  Purchase #4 $159.69   4.554%   $166.9623   $166.96   $166.95   $167.00  
  Purchase #5 $75.88   11.135%   $84.3292   $84.33   $84.35   $84.30  
  Purchase #6 $187.92   4.520%   $196.414   $196.41   $196.40   $196.40  
  Purchase #7 $239.68   9.728%   $262.9961   $263.00   $263.00   $263.00  
  7 purchase totals = $1,121.43       $1,230.2198   $1,230.21   $1,230.20   $1,230.30