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 $148.33   11.270%   $165.0468   $165.05   $165.05   $165.00  
  Purchase #2 $90.41   12.786%   $101.9698   $101.97   $101.95   $102.00  
  Purchase #3 $129.33   9.762%   $141.9552   $141.96   $141.95   $142.00  
  Purchase #4 $168.69   9.491%   $184.7004   $184.70   $184.70   $184.70  
  Purchase #5 $184.62   10.551%   $204.0993   $204.10   $204.10   $204.10  
  Purchase #6 $142.91   8.231%   $154.6729   $154.67   $154.65   $154.70  
  Purchase #7 $87.86   4.553%   $91.8603   $91.86   $91.85   $91.90  
  7 purchase totals = $952.15       $1,044.3047   $1,044.31   $1,044.25   $1,044.40