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 $162.66   11.839%   $181.9173   $181.92   $181.90   $181.90  
  Purchase #2 $219.94   5.145%   $231.2559   $231.26   $231.25   $231.30  
  Purchase #3 $228.33   5.450%   $240.774   $240.77   $240.75   $240.80  
  Purchase #4 $33.72   7.358%   $36.2011   $36.20   $36.20   $36.20  
  Purchase #5 $208.68   5.167%   $219.4625   $219.46   $219.45   $219.50  
  Purchase #6 $104.91   12.664%   $118.1958   $118.20   $118.20   $118.20  
  Purchase #7 $10.75   11.224%   $11.9566   $11.96   $11.95   $12.00  
  7 purchase totals = $968.99       $1,039.7632   $1,039.77   $1,039.70   $1,039.90