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 $143.43   13.512%   $162.8103   $162.81   $162.80   $162.80  
  Purchase #2 $33.37   8.167%   $36.0953   $36.10   $36.10   $36.10  
  Purchase #3 $32.27   13.488%   $36.6226   $36.62   $36.60   $36.60  
  Purchase #4 $225.77   6.611%   $240.6957   $240.70   $240.70   $240.70  
  Purchase #5 $180.36   13.611%   $204.9088   $204.91   $204.90   $204.90  
  Purchase #6 $163.76   7.370%   $175.8291   $175.83   $175.85   $175.80  
  Purchase #7 $93.37   8.558%   $101.3606   $101.36   $101.35   $101.40  
  7 purchase totals = $872.33       $958.3224   $958.33   $958.30   $958.30