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 $161.77   13.861%   $184.1929   $184.19   $184.20   $184.20  
  Purchase #2 $172.55   8.770%   $187.6826   $187.68   $187.70   $187.70  
  Purchase #3 $23.33   12.212%   $26.1791   $26.18   $26.20   $26.20  
  Purchase #4 $119.29   5.713%   $126.105   $126.11   $126.10   $126.10  
  Purchase #5 $191.80   12.188%   $215.1766   $215.18   $215.20   $215.20  
  Purchase #6 $64.41   5.393%   $67.8836   $67.88   $67.90   $67.90  
  Purchase #7 $48.46   12.632%   $54.5815   $54.58   $54.60   $54.60  
  7 purchase totals = $781.61       $861.8013   $861.80   $861.90   $861.90