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 $206.55   13.278%   $233.9757   $233.98   $234.00   $234.00  
  Purchase #2 $77.49   4.748%   $81.1692   $81.17   $81.15   $81.20  
  Purchase #3 $74.76   12.398%   $84.0287   $84.03   $84.05   $84.00  
  Purchase #4 $183.76   10.214%   $202.5292   $202.53   $202.55   $202.50  
  Purchase #5 $229.56   4.696%   $240.3401   $240.34   $240.35   $240.30  
  Purchase #6 $204.88   9.287%   $223.9072   $223.91   $223.90   $223.90  
  Purchase #7 $77.34   7.393%   $83.0577   $83.06   $83.05   $83.10  
  7 purchase totals = $1,054.34       $1,149.0078   $1,149.02   $1,149.05   $1,149.00