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 $65.62   11.785%   $73.3533   $73.35   $73.35   $73.40  
  Purchase #2 $153.52   10.234%   $169.2312   $169.23   $169.25   $169.20  
  Purchase #3 $93.78   8.608%   $101.8526   $101.85   $101.85   $101.90  
  Purchase #4 $208.70   10.515%   $230.6448   $230.64   $230.65   $230.60  
  Purchase #5 $210.60   10.783%   $233.309   $233.31   $233.30   $233.30  
  Purchase #6 $147.72   13.523%   $167.6962   $167.70   $167.70   $167.70  
  Purchase #7 $223.75   8.176%   $242.0438   $242.04   $242.05   $242.00  
  7 purchase totals = $1,103.69       $1,218.1309   $1,218.12   $1,218.15   $1,218.10