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 $89.25   7.327%   $95.7893   $95.79   $95.80   $95.80  
  Purchase #2 $138.88   9.804%   $152.4958   $152.50   $152.50   $152.50  
  Purchase #3 $179.83   7.381%   $193.1033   $193.10   $193.10   $193.10  
  Purchase #4 $64.85   7.265%   $69.5614   $69.56   $69.55   $69.60  
  Purchase #5 $85.99   9.666%   $94.3018   $94.30   $94.30   $94.30  
  Purchase #6 $153.46   11.709%   $171.4286   $171.43   $171.45   $171.40  
  Purchase #7 $15.85   12.442%   $17.8221   $17.82   $17.80   $17.80  
  7 purchase totals = $728.11       $794.5023   $794.50   $794.50   $794.50