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 $159.67   10.564%   $176.5375   $176.54   $176.55   $176.50  
  Purchase #2 $211.74   11.773%   $236.6682   $236.67   $236.65   $236.70  
  Purchase #3 $206.63   6.110%   $219.2551   $219.26   $219.25   $219.30  
  Purchase #4 $149.98   11.562%   $167.3207   $167.32   $167.30   $167.30  
  Purchase #5 $153.25   11.722%   $171.214   $171.21   $171.20   $171.20  
  Purchase #6 $46.98   8.474%   $50.9611   $50.96   $50.95   $51.00  
  Purchase #7 $27.27   6.718%   $29.102   $29.10   $29.10   $29.10  
  7 purchase totals = $955.52       $1,051.0586   $1,051.06   $1,051.00   $1,051.10