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 $86.34   13.548%   $98.0373   $98.04   $98.05   $98.00  
  Purchase #2 $47.58   4.214%   $49.585   $49.59   $49.60   $49.60  
  Purchase #3 $247.33   9.478%   $270.7719   $270.77   $270.75   $270.80  
  Purchase #4 $34.74   4.228%   $36.2088   $36.21   $36.20   $36.20  
  Purchase #5 $147.69   13.598%   $167.7729   $167.77   $167.75   $167.80  
  Purchase #6 $214.65   13.809%   $244.291   $244.29   $244.30   $244.30  
  Purchase #7 $189.40   13.522%   $215.0107   $215.01   $215.00   $215.00  
  7 purchase totals = $967.73       $1,081.6776   $1,081.68   $1,081.65   $1,081.70