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 $66.25   10.261%   $73.0479   $73.05   $73.05   $73.00  
  Purchase #2 $119.53   4.478%   $124.8826   $124.88   $124.90   $124.90  
  Purchase #3 $9.48   6.442%   $10.0907   $10.09   $10.10   $10.10  
  Purchase #4 $178.72   5.368%   $188.3137   $188.31   $188.30   $188.30  
  Purchase #5 $53.46   9.177%   $58.366   $58.37   $58.35   $58.40  
  Purchase #6 $243.48   3.452%   $251.8849   $251.88   $251.90   $251.90  
  Purchase #7 $80.28   5.539%   $84.7267   $84.73   $84.75   $84.70  
  7 purchase totals = $751.20       $791.3125   $791.31   $791.35   $791.30