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 $57.41   11.147%   $63.8095   $63.81   $63.80   $63.80  
  Purchase #2 $124.83   11.563%   $139.2641   $139.26   $139.25   $139.30  
  Purchase #3 $95.57   11.322%   $106.3904   $106.39   $106.40   $106.40  
  Purchase #4 $63.45   6.168%   $67.3636   $67.36   $67.35   $67.40  
  Purchase #5 $53.46   9.521%   $58.5499   $58.55   $58.55   $58.50  
  Purchase #6 $153.81   8.754%   $167.2745   $167.27   $167.25   $167.30  
  Purchase #7 $145.36   4.455%   $151.8358   $151.84   $151.85   $151.80  
  7 purchase totals = $693.89       $754.4878   $754.48   $754.45   $754.50