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 $247.63   11.116%   $275.1566   $275.16   $275.15   $275.20  
  Purchase #2 $162.69   12.791%   $183.4997   $183.50   $183.50   $183.50  
  Purchase #3 $52.83   9.295%   $57.7405   $57.74   $57.75   $57.70  
  Purchase #4 $238.35   12.184%   $267.3906   $267.39   $267.40   $267.40  
  Purchase #5 $133.88   12.735%   $150.9296   $150.93   $150.95   $150.90  
  Purchase #6 $62.60   13.865%   $71.2795   $71.28   $71.30   $71.30  
  Purchase #7 $220.96   12.450%   $248.4695   $248.47   $248.45   $248.50  
  7 purchase totals = $1,118.94       $1,254.4660   $1,254.47   $1,254.50   $1,254.50