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 $125.49   6.595%   $133.7661   $133.77   $133.75   $133.80  
  Purchase #2 $100.49   11.118%   $111.6625   $111.66   $111.65   $111.70  
  Purchase #3 $70.53   5.781%   $74.6073   $74.61   $74.60   $74.60  
  Purchase #4 $167.28   7.150%   $179.2405   $179.24   $179.25   $179.20  
  Purchase #5 $124.48   6.214%   $132.2152   $132.22   $132.20   $132.20  
  Purchase #6 $19.49   11.206%   $21.674   $21.67   $21.65   $21.70  
  Purchase #7 $213.61   12.541%   $240.3988   $240.40   $240.40   $240.40  
  7 purchase totals = $821.37       $893.5644   $893.57   $893.50   $893.60