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 $113.74   4.527%   $118.889   $118.89   $118.90   $118.90  
  Purchase #2 $211.37   13.400%   $239.6936   $239.69   $239.70   $239.70  
  Purchase #3 $189.45   3.440%   $195.9671   $195.97   $195.95   $196.00  
  Purchase #4 $47.92   11.832%   $53.5899   $53.59   $53.60   $53.60  
  Purchase #5 $116.60   8.573%   $126.5961   $126.60   $126.60   $126.60  
  Purchase #6 $177.65   3.713%   $184.2461   $184.25   $184.25   $184.20  
  Purchase #7 $115.27   9.472%   $126.1884   $126.19   $126.20   $126.20  
  7 purchase totals = $972.00       $1,045.1702   $1,045.18   $1,045.20   $1,045.20