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 $60.38   10.281%   $66.5877   $66.59   $66.60   $66.60  
  Purchase #2 $165.39   11.121%   $183.783   $183.78   $183.80   $183.80  
  Purchase #3 $178.96   12.190%   $200.7752   $200.78   $200.80   $200.80  
  Purchase #4 $249.81   6.366%   $265.7129   $265.71   $265.70   $265.70  
  Purchase #5 $145.99   8.609%   $158.5583   $158.56   $158.55   $158.60  
  Purchase #6 $174.60   10.775%   $193.4132   $193.41   $193.40   $193.40  
  Purchase #7 $13.57   12.713%   $15.2952   $15.30   $15.30   $15.30  
  7 purchase totals = $988.70       $1,084.1255   $1,084.13   $1,084.15   $1,084.20