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 $122.87   11.684%   $137.2261   $137.23   $137.25   $137.20  
  Purchase #2 $155.98   9.169%   $170.2818   $170.28   $170.30   $170.30  
  Purchase #3 $106.60   3.436%   $110.2628   $110.26   $110.25   $110.30  
  Purchase #4 $208.35   12.593%   $234.5875   $234.59   $234.60   $234.60  
  Purchase #5 $51.45   6.826%   $54.962   $54.96   $54.95   $55.00  
  Purchase #6 $118.25   12.313%   $132.8101   $132.81   $132.80   $132.80  
  Purchase #7 $206.30   3.553%   $213.6298   $213.63   $213.65   $213.60  
  7 purchase totals = $969.80       $1,053.7601   $1,053.76   $1,053.80   $1,053.80