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 $208.76   8.149%   $225.7719   $225.77   $225.75   $225.80  
  Purchase #2 $128.79   12.226%   $144.5359   $144.54   $144.55   $144.50  
  Purchase #3 $234.87   12.269%   $263.6862   $263.69   $263.70   $263.70  
  Purchase #4 $61.39   13.244%   $69.5205   $69.52   $69.50   $69.50  
  Purchase #5 $62.91   3.296%   $64.9835   $64.98   $65.00   $65.00  
  Purchase #6 $148.37   4.411%   $154.9146   $154.91   $154.90   $154.90  
  Purchase #7 $214.91   8.792%   $233.8049   $233.80   $233.80   $233.80  
  7 purchase totals = $1,060.00       $1,157.2175   $1,157.21   $1,157.20   $1,157.20