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 $118.92   11.142%   $132.1701   $132.17   $132.15   $132.20  
  Purchase #2 $122.27   12.320%   $137.3337   $137.33   $137.35   $137.30  
  Purchase #3 $242.51   10.591%   $268.1942   $268.19   $268.20   $268.20  
  Purchase #4 $176.25   3.207%   $181.9023   $181.90   $181.90   $181.90  
  Purchase #5 $73.54   10.508%   $81.2676   $81.27   $81.25   $81.30  
  Purchase #6 $97.57   11.743%   $109.0276   $109.03   $109.05   $109.00  
  Purchase #7 $146.29   13.492%   $166.0274   $166.03   $166.05   $166.00  
  7 purchase totals = $977.35       $1,075.9229   $1,075.92   $1,075.95   $1,075.90