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 $52.37   6.528%   $55.7887   $55.79   $55.80   $55.80  
  Purchase #2 $216.61   7.613%   $233.1005   $233.10   $233.10   $233.10  
  Purchase #3 $248.70   3.557%   $257.5463   $257.55   $257.55   $257.50  
  Purchase #4 $16.29   12.616%   $18.3451   $18.35   $18.35   $18.30  
  Purchase #5 $11.95   13.510%   $13.5644   $13.56   $13.55   $13.60  
  Purchase #6 $134.89   4.835%   $141.4119   $141.41   $141.40   $141.40  
  Purchase #7 $18.28   4.338%   $19.073   $19.07   $19.05   $19.10  
  7 purchase totals = $699.09       $738.8299   $738.83   $738.80   $738.80