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 $216.98   4.177%   $226.0433   $226.04   $226.05   $226.00  
  Purchase #2 $208.33   12.190%   $233.7254   $233.73   $233.75   $233.70  
  Purchase #3 $187.76   8.666%   $204.0313   $204.03   $204.05   $204.00  
  Purchase #4 $22.99   11.197%   $25.5642   $25.56   $25.55   $25.60  
  Purchase #5 $161.34   3.486%   $166.9643   $166.96   $166.95   $167.00  
  Purchase #6 $12.62   10.253%   $13.9139   $13.91   $13.90   $13.90  
  Purchase #7 $83.84   8.784%   $91.2045   $91.20   $91.20   $91.20  
  7 purchase totals = $893.86       $961.4469   $961.43   $961.45   $961.40