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 $161.33   12.606%   $181.6673   $181.67   $181.65   $181.70  
  Purchase #2 $108.56   8.291%   $117.5607   $117.56   $117.55   $117.60  
  Purchase #3 $142.30   4.565%   $148.796   $148.80   $148.80   $148.80  
  Purchase #4 $129.77   7.183%   $139.0914   $139.09   $139.10   $139.10  
  Purchase #5 $56.72   11.225%   $63.0868   $63.09   $63.10   $63.10  
  Purchase #6 $184.57   4.516%   $192.9052   $192.91   $192.90   $192.90  
  Purchase #7 $204.48   6.181%   $217.1189   $217.12   $217.10   $217.10  
  7 purchase totals = $987.73       $1,060.2263   $1,060.24   $1,060.20   $1,060.30