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 $92.40   10.675%   $102.2637   $102.26   $102.25   $102.30  
  Purchase #2 $160.53   12.695%   $180.9093   $180.91   $180.90   $180.90  
  Purchase #3 $192.35   7.842%   $207.4341   $207.43   $207.45   $207.40  
  Purchase #4 $87.80   7.467%   $94.356   $94.36   $94.35   $94.40  
  Purchase #5 $214.71   6.444%   $228.5459   $228.55   $228.55   $228.50  
  Purchase #6 $139.93   12.490%   $157.4073   $157.41   $157.40   $157.40  
  Purchase #7 $234.38   9.155%   $255.8375   $255.84   $255.85   $255.80  
  7 purchase totals = $1,122.10       $1,226.7538   $1,226.76   $1,226.75   $1,226.70