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 $162.49   13.554%   $184.5139   $184.51   $184.50   $184.50  
  Purchase #2 $41.38   4.188%   $43.113   $43.11   $43.10   $43.10  
  Purchase #3 $202.36   11.795%   $226.2284   $226.23   $226.25   $226.20  
  Purchase #4 $213.70   9.579%   $234.1703   $234.17   $234.15   $234.20  
  Purchase #5 $18.94   4.830%   $19.8548   $19.85   $19.85   $19.90  
  Purchase #6 $165.81   4.764%   $173.7092   $173.71   $173.70   $173.70  
  Purchase #7 $232.97   13.727%   $264.9498   $264.95   $264.95   $264.90  
  7 purchase totals = $1,037.65       $1,146.5394   $1,146.53   $1,146.50   $1,146.50