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 $18.37   8.192%   $19.8749   $19.87   $19.85   $19.90  
  Purchase #2 $119.25   13.783%   $135.6862   $135.69   $135.70   $135.70  
  Purchase #3 $15.96   13.513%   $18.1167   $18.12   $18.10   $18.10  
  Purchase #4 $172.69   11.263%   $192.1401   $192.14   $192.15   $192.10  
  Purchase #5 $120.93   7.572%   $130.0868   $130.09   $130.10   $130.10  
  Purchase #6 $211.84   10.729%   $234.5683   $234.57   $234.55   $234.60  
  Purchase #7 $75.53   4.127%   $78.6471   $78.65   $78.65   $78.60  
  7 purchase totals = $734.57       $809.1201   $809.13   $809.10   $809.10