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 $209.65   11.871%   $234.5376   $234.54   $234.55   $234.50  
  Purchase #2 $205.97   13.386%   $233.5411   $233.54   $233.55   $233.50  
  Purchase #3 $52.48   11.703%   $58.6217   $58.62   $58.60   $58.60  
  Purchase #4 $110.84   4.607%   $115.9464   $115.95   $115.95   $115.90  
  Purchase #5 $160.48   7.670%   $172.7888   $172.79   $172.80   $172.80  
  Purchase #6 $120.77   5.664%   $127.6104   $127.61   $127.60   $127.60  
  Purchase #7 $63.26   7.370%   $67.9223   $67.92   $67.90   $67.90  
  7 purchase totals = $923.45       $1,010.9683   $1,010.97   $1,010.95   $1,010.80