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 $85.91   12.723%   $96.8403   $96.84   $96.85   $96.80  
  Purchase #2 $23.60   9.107%   $25.7493   $25.75   $25.75   $25.70  
  Purchase #3 $155.69   4.865%   $163.2643   $163.26   $163.25   $163.30  
  Purchase #4 $141.73   10.829%   $157.0779   $157.08   $157.10   $157.10  
  Purchase #5 $161.91   8.431%   $175.5606   $175.56   $175.55   $175.60  
  Purchase #6 $186.33   9.434%   $203.9084   $203.91   $203.90   $203.90  
  Purchase #7 $104.80   13.161%   $118.5927   $118.59   $118.60   $118.60  
  7 purchase totals = $859.97       $940.9935   $940.99   $941.00   $941.00