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 $82.52   7.426%   $88.6479   $88.65   $88.65   $88.60  
  Purchase #2 $135.41   13.697%   $153.9571   $153.96   $153.95   $154.00  
  Purchase #3 $179.53   5.123%   $188.7273   $188.73   $188.75   $188.70  
  Purchase #4 $174.73   5.817%   $184.894   $184.89   $184.90   $184.90  
  Purchase #5 $247.57   7.797%   $266.873   $266.87   $266.85   $266.90  
  Purchase #6 $207.48   8.703%   $225.537   $225.54   $225.55   $225.50  
  Purchase #7 $158.40   5.462%   $167.0518   $167.05   $167.05   $167.10  
  7 purchase totals = $1,185.64       $1,275.6881   $1,275.69   $1,275.70   $1,275.70