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 $232.84   13.726%   $264.7996   $264.80   $264.80   $264.80  
  Purchase #2 $188.47   12.696%   $212.3982   $212.40   $212.40   $212.40  
  Purchase #3 $149.31   12.727%   $168.3127   $168.31   $168.30   $168.30  
  Purchase #4 $56.87   13.134%   $64.3393   $64.34   $64.35   $64.30  
  Purchase #5 $160.86   12.361%   $180.7439   $180.74   $180.75   $180.70  
  Purchase #6 $127.51   11.393%   $142.0372   $142.04   $142.05   $142.00  
  Purchase #7 $22.77   7.652%   $24.5124   $24.51   $24.50   $24.50  
  7 purchase totals = $938.63       $1,057.1433   $1,057.14   $1,057.15   $1,057.00