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 $114.55   5.552%   $120.9098   $120.91   $120.90   $120.90  
  Purchase #2 $191.85   7.818%   $206.8488   $206.85   $206.85   $206.80  
  Purchase #3 $109.97   5.429%   $115.9403   $115.94   $115.95   $115.90  
  Purchase #4 $113.29   9.684%   $124.261   $124.26   $124.25   $124.30  
  Purchase #5 $154.96   7.428%   $166.4704   $166.47   $166.45   $166.50  
  Purchase #6 $55.68   4.423%   $58.1427   $58.14   $58.15   $58.10  
  Purchase #7 $120.73   4.590%   $126.2715   $126.27   $126.25   $126.30  
  7 purchase totals = $861.03       $918.8445   $918.84   $918.80   $918.80