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 $189.25   8.476%   $205.2908   $205.29   $205.30   $205.30  
  Purchase #2 $64.31   3.110%   $66.31   $66.31   $66.30   $66.30  
  Purchase #3 $159.69   5.137%   $167.8933   $167.89   $167.90   $167.90  
  Purchase #4 $213.53   7.333%   $229.1882   $229.19   $229.20   $229.20  
  Purchase #5 $53.70   9.262%   $58.6737   $58.67   $58.65   $58.70  
  Purchase #6 $213.48   8.823%   $232.3153   $232.32   $232.30   $232.30  
  Purchase #7 $151.58   3.124%   $156.3154   $156.32   $156.30   $156.30  
  7 purchase totals = $1,045.54       $1,115.9867   $1,115.99   $1,115.95   $1,116.00