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 $203.78   13.749%   $231.7977   $231.80   $231.80   $231.80  
  Purchase #2 $88.61   8.825%   $96.4298   $96.43   $96.45   $96.40  
  Purchase #3 $85.82   4.752%   $89.8982   $89.90   $89.90   $89.90  
  Purchase #4 $190.43   5.679%   $201.2445   $201.24   $201.25   $201.20  
  Purchase #5 $144.62   12.405%   $162.5601   $162.56   $162.55   $162.60  
  Purchase #6 $187.47   8.158%   $202.7638   $202.76   $202.75   $202.80  
  Purchase #7 $23.62   13.776%   $26.8739   $26.87   $26.85   $26.90  
  7 purchase totals = $924.35       $1,011.5680   $1,011.56   $1,011.55   $1,011.60