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 $18.33   7.279%   $19.6642   $19.66   $19.65   $19.70  
  Purchase #2 $201.99   4.463%   $211.0048   $211.00   $211.00   $211.00  
  Purchase #3 $149.97   10.393%   $165.5564   $165.56   $165.55   $165.60  
  Purchase #4 $224.44   6.638%   $239.3383   $239.34   $239.35   $239.30  
  Purchase #5 $186.33   8.247%   $201.6966   $201.70   $201.70   $201.70  
  Purchase #6 $151.32   6.744%   $161.525   $161.53   $161.55   $161.50  
  Purchase #7 $23.72   5.504%   $25.0255   $25.03   $25.05   $25.00  
  7 purchase totals = $956.10       $1,023.8108   $1,023.82   $1,023.85   $1,023.80