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 $243.67   6.306%   $259.0358   $259.04   $259.05   $259.00  
  Purchase #2 $216.72   4.722%   $226.9535   $226.95   $226.95   $227.00  
  Purchase #3 $194.38   5.106%   $204.305   $204.31   $204.30   $204.30  
  Purchase #4 $213.64   5.723%   $225.8666   $225.87   $225.85   $225.90  
  Purchase #5 $126.83   4.629%   $132.701   $132.70   $132.70   $132.70  
  Purchase #6 $202.25   5.117%   $212.5991   $212.60   $212.60   $212.60  
  Purchase #7 $235.91   7.383%   $253.3272   $253.33   $253.35   $253.30  
  7 purchase totals = $1,433.40       $1,514.7882   $1,514.80   $1,514.80   $1,514.80