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 $237.58   8.256%   $257.1946   $257.19   $257.20   $257.20  
  Purchase #2 $202.49   4.517%   $211.6365   $211.64   $211.65   $211.60  
  Purchase #3 $108.59   4.661%   $113.6514   $113.65   $113.65   $113.70  
  Purchase #4 $244.72   13.556%   $277.8942   $277.89   $277.90   $277.90  
  Purchase #5 $203.58   12.652%   $229.3369   $229.34   $229.35   $229.30  
  Purchase #6 $200.30   11.173%   $222.6795   $222.68   $222.70   $222.70  
  Purchase #7 $87.57   6.667%   $93.4083   $93.41   $93.40   $93.40  
  7 purchase totals = $1,284.83       $1,405.8014   $1,405.80   $1,405.85   $1,405.80