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 $46.65   12.632%   $52.5428   $52.54   $52.55   $52.50  
  Purchase #2 $237.26   6.517%   $252.7222   $252.72   $252.70   $252.70  
  Purchase #3 $197.69   5.126%   $207.8236   $207.82   $207.80   $207.80  
  Purchase #4 $101.82   4.276%   $106.1738   $106.17   $106.15   $106.20  
  Purchase #5 $192.37   5.294%   $202.5541   $202.55   $202.55   $202.60  
  Purchase #6 $55.59   13.339%   $63.0052   $63.01   $63.00   $63.00  
  Purchase #7 $39.97   6.762%   $42.6728   $42.67   $42.65   $42.70  
  7 purchase totals = $871.35       $927.4945   $927.48   $927.40   $927.50