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 $78.43   13.228%   $88.8047   $88.80   $88.80   $88.80  
  Purchase #2 $196.89   11.563%   $219.6564   $219.66   $219.65   $219.70  
  Purchase #3 $213.29   12.497%   $239.9449   $239.94   $239.95   $239.90  
  Purchase #4 $71.74   7.201%   $76.906   $76.91   $76.90   $76.90  
  Purchase #5 $105.70   7.663%   $113.7998   $113.80   $113.80   $113.80  
  Purchase #6 $249.47   11.299%   $277.6576   $277.66   $277.65   $277.70  
  Purchase #7 $30.82   13.605%   $35.0131   $35.01   $35.00   $35.00  
  7 purchase totals = $946.34       $1,051.7825   $1,051.78   $1,051.75   $1,051.80