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 $61.88   8.371%   $67.06   $67.06   $67.05   $67.10  
  Purchase #2 $168.26   7.716%   $181.2429   $181.24   $181.25   $181.20  
  Purchase #3 $136.62   9.288%   $149.3093   $149.31   $149.30   $149.30  
  Purchase #4 $175.96   4.626%   $184.0999   $184.10   $184.10   $184.10  
  Purchase #5 $231.62   5.728%   $244.8872   $244.89   $244.90   $244.90  
  Purchase #6 $195.56   11.239%   $217.539   $217.54   $217.55   $217.50  
  Purchase #7 $121.30   11.835%   $135.6559   $135.66   $135.65   $135.70  
  7 purchase totals = $1,091.20       $1,179.7942   $1,179.80   $1,179.80   $1,179.80