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 $154.64   13.554%   $175.5999   $175.60   $175.60   $175.60  
  Purchase #2 $120.90   4.658%   $126.5315   $126.53   $126.55   $126.50  
  Purchase #3 $226.77   11.581%   $253.0322   $253.03   $253.05   $253.00  
  Purchase #4 $105.33   11.861%   $117.8232   $117.82   $117.80   $117.80  
  Purchase #5 $171.68   10.694%   $190.0395   $190.04   $190.05   $190.00  
  Purchase #6 $63.58   6.240%   $67.5474   $67.55   $67.55   $67.50  
  Purchase #7 $64.73   7.801%   $69.7796   $69.78   $69.80   $69.80  
  7 purchase totals = $907.63       $1,000.3533   $1,000.35   $1,000.40   $1,000.20