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 $240.86   9.247%   $263.1323   $263.13   $263.15   $263.10  
  Purchase #2 $246.85   3.447%   $255.3589   $255.36   $255.35   $255.40  
  Purchase #3 $135.68   13.801%   $154.4052   $154.41   $154.40   $154.40  
  Purchase #4 $244.92   5.855%   $259.2601   $259.26   $259.25   $259.30  
  Purchase #5 $210.25   3.107%   $216.7825   $216.78   $216.80   $216.80  
  Purchase #6 $181.44   11.638%   $202.556   $202.56   $202.55   $202.60  
  Purchase #7 $52.65   10.235%   $58.0387   $58.04   $58.05   $58.00  
  7 purchase totals = $1,312.65       $1,409.5337   $1,409.54   $1,409.55   $1,409.60