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 $165.84   10.146%   $182.6661   $182.67   $182.65   $182.70  
  Purchase #2 $13.47   8.583%   $14.6261   $14.63   $14.65   $14.60  
  Purchase #3 $57.96   6.156%   $61.528   $61.53   $61.55   $61.50  
  Purchase #4 $67.40   9.434%   $73.7585   $73.76   $73.75   $73.80  
  Purchase #5 $216.80   9.400%   $237.1792   $237.18   $237.20   $237.20  
  Purchase #6 $235.37   13.595%   $267.3686   $267.37   $267.35   $267.40  
  Purchase #7 $218.50   3.290%   $225.6887   $225.69   $225.70   $225.70  
  7 purchase totals = $975.34       $1,062.8152   $1,062.83   $1,062.85   $1,062.90