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 $82.62   3.629%   $85.6183   $85.62   $85.60   $85.60  
  Purchase #2 $177.34   4.290%   $184.9479   $184.95   $184.95   $184.90  
  Purchase #3 $73.74   4.166%   $76.812   $76.81   $76.80   $76.80  
  Purchase #4 $166.27   10.357%   $183.4906   $183.49   $183.50   $183.50  
  Purchase #5 $80.84   4.323%   $84.3347   $84.33   $84.35   $84.30  
  Purchase #6 $28.98   10.791%   $32.1072   $32.11   $32.10   $32.10  
  Purchase #7 $164.84   8.604%   $179.0228   $179.02   $179.00   $179.00  
  7 purchase totals = $774.63       $826.3335   $826.33   $826.30   $826.20