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 $94.97   12.412%   $106.7577   $106.76   $106.75   $106.80  
  Purchase #2 $137.94   3.551%   $142.8382   $142.84   $142.85   $142.80  
  Purchase #3 $195.96   5.448%   $206.6359   $206.64   $206.65   $206.60  
  Purchase #4 $246.85   9.579%   $270.4958   $270.50   $270.50   $270.50  
  Purchase #5 $203.44   9.262%   $222.2826   $222.28   $222.30   $222.30  
  Purchase #6 $203.62   11.177%   $226.3786   $226.38   $226.40   $226.40  
  Purchase #7 $167.58   4.462%   $175.0574   $175.06   $175.05   $175.10  
  7 purchase totals = $1,250.36       $1,350.4462   $1,350.46   $1,350.50   $1,350.50