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 $23.97   9.592%   $26.2692   $26.27   $26.25   $26.30  
  Purchase #2 $244.32   6.623%   $260.5013   $260.50   $260.50   $260.50  
  Purchase #3 $129.94   9.643%   $142.4701   $142.47   $142.45   $142.50  
  Purchase #4 $120.43   12.700%   $135.7246   $135.72   $135.70   $135.70  
  Purchase #5 $188.63   6.775%   $201.4097   $201.41   $201.40   $201.40  
  Purchase #6 $119.86   3.534%   $124.0959   $124.10   $124.10   $124.10  
  Purchase #7 $157.99   5.548%   $166.7553   $166.76   $166.75   $166.80  
  7 purchase totals = $985.14       $1,057.2261   $1,057.23   $1,057.15   $1,057.30