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 $66.59   9.843%   $73.1445   $73.14   $73.15   $73.10  
  Purchase #2 $113.32   8.798%   $123.2899   $123.29   $123.30   $123.30  
  Purchase #3 $248.65   6.665%   $265.2225   $265.22   $265.20   $265.20  
  Purchase #4 $56.72   7.784%   $61.1351   $61.14   $61.15   $61.10  
  Purchase #5 $139.33   10.566%   $154.0516   $154.05   $154.05   $154.10  
  Purchase #6 $222.86   11.185%   $247.7869   $247.79   $247.80   $247.80  
  Purchase #7 $220.70   5.555%   $232.9599   $232.96   $232.95   $233.00  
  7 purchase totals = $1,068.17       $1,157.5904   $1,157.59   $1,157.60   $1,157.60