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 $198.85   12.299%   $223.3066   $223.31   $223.30   $223.30  
  Purchase #2 $87.85   11.392%   $97.8579   $97.86   $97.85   $97.90  
  Purchase #3 $208.91   11.705%   $233.3629   $233.36   $233.35   $233.40  
  Purchase #4 $192.96   5.860%   $204.2675   $204.27   $204.25   $204.30  
  Purchase #5 $54.67   5.771%   $57.825   $57.83   $57.85   $57.80  
  Purchase #6 $218.54   11.499%   $243.6699   $243.67   $243.65   $243.70  
  Purchase #7 $60.25   10.174%   $66.3798   $66.38   $66.40   $66.40  
  7 purchase totals = $1,022.03       $1,126.6696   $1,126.68   $1,126.65   $1,126.80