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 $197.68   6.749%   $211.0214   $211.02   $211.00   $211.00  
  Purchase #2 $70.44   3.276%   $72.7476   $72.75   $72.75   $72.70  
  Purchase #3 $17.82   8.278%   $19.2951   $19.30   $19.30   $19.30  
  Purchase #4 $82.25   5.790%   $87.0123   $87.01   $87.00   $87.00  
  Purchase #5 $115.72   9.444%   $126.6486   $126.65   $126.65   $126.60  
  Purchase #6 $32.73   7.266%   $35.1082   $35.11   $35.10   $35.10  
  Purchase #7 $61.62   8.254%   $66.7061   $66.71   $66.70   $66.70  
  7 purchase totals = $578.26       $618.5393   $618.55   $618.50   $618.40