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 $191.29   9.232%   $208.9499   $208.95   $208.95   $208.90  
  Purchase #2 $33.87   4.767%   $35.4846   $35.48   $35.50   $35.50  
  Purchase #3 $202.90   10.414%   $224.03   $224.03   $224.05   $224.00  
  Purchase #4 $213.86   10.747%   $236.8435   $236.84   $236.85   $236.80  
  Purchase #5 $116.78   5.481%   $123.1807   $123.18   $123.20   $123.20  
  Purchase #6 $206.29   9.334%   $225.5451   $225.55   $225.55   $225.50  
  Purchase #7 $179.99   7.612%   $193.6908   $193.69   $193.70   $193.70  
  7 purchase totals = $1,144.98       $1,247.7246   $1,247.72   $1,247.80   $1,247.60