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 $166.27   12.851%   $187.6374   $187.64   $187.65   $187.60  
  Purchase #2 $187.76   9.179%   $204.9945   $204.99   $205.00   $205.00  
  Purchase #3 $184.68   7.418%   $198.3796   $198.38   $198.40   $198.40  
  Purchase #4 $111.87   10.119%   $123.1901   $123.19   $123.20   $123.20  
  Purchase #5 $187.83   3.550%   $194.498   $194.50   $194.50   $194.50  
  Purchase #6 $67.56   12.790%   $76.2009   $76.20   $76.20   $76.20  
  Purchase #7 $145.83   11.528%   $162.6413   $162.64   $162.65   $162.60  
  7 purchase totals = $1,051.80       $1,147.5418   $1,147.54   $1,147.60   $1,147.50