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 $126.99   11.194%   $141.2053   $141.21   $141.20   $141.20  
  Purchase #2 $138.87   6.831%   $148.3562   $148.36   $148.35   $148.40  
  Purchase #3 $82.64   5.461%   $87.153   $87.15   $87.15   $87.20  
  Purchase #4 $51.53   5.702%   $54.4682   $54.47   $54.45   $54.50  
  Purchase #5 $119.82   11.135%   $133.162   $133.16   $133.15   $133.20  
  Purchase #6 $200.68   4.745%   $210.2023   $210.20   $210.20   $210.20  
  Purchase #7 $118.46   3.854%   $123.0254   $123.03   $123.05   $123.00  
  7 purchase totals = $838.99       $897.5724   $897.58   $897.55   $897.70