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 $250.42   12.539%   $281.8202   $281.82   $281.80   $281.80  
  Purchase #2 $54.48   13.716%   $61.9525   $61.95   $61.95   $62.00  
  Purchase #3 $227.41   12.188%   $255.1267   $255.13   $255.15   $255.10  
  Purchase #4 $26.54   3.701%   $27.5222   $27.52   $27.50   $27.50  
  Purchase #5 $161.42   5.650%   $170.5402   $170.54   $170.55   $170.50  
  Purchase #6 $136.63   5.574%   $144.2458   $144.25   $144.25   $144.20  
  Purchase #7 $220.59   8.813%   $240.0306   $240.03   $240.05   $240.00  
  7 purchase totals = $1,077.49       $1,181.2382   $1,181.24   $1,181.25   $1,181.10