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 $216.36   8.211%   $234.1253   $234.13   $234.15   $234.10  
  Purchase #2 $191.54   6.155%   $203.3293   $203.33   $203.35   $203.30  
  Purchase #3 $203.41   6.850%   $217.3436   $217.34   $217.35   $217.30  
  Purchase #4 $206.35   4.215%   $215.0477   $215.05   $215.05   $215.00  
  Purchase #5 $28.25   4.478%   $29.515   $29.52   $29.50   $29.50  
  Purchase #6 $114.38   3.587%   $118.4828   $118.48   $118.50   $118.50  
  Purchase #7 $36.40   10.454%   $40.2053   $40.21   $40.20   $40.20  
  7 purchase totals = $996.69       $1,058.0490   $1,058.06   $1,058.10   $1,057.90