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 $135.97   13.770%   $154.6931   $154.69   $154.70   $154.70  
  Purchase #2 $249.54   9.112%   $272.2781   $272.28   $272.30   $272.30  
  Purchase #3 $42.45   11.331%   $47.26   $47.26   $47.25   $47.30  
  Purchase #4 $182.29   13.289%   $206.5145   $206.51   $206.50   $206.50  
  Purchase #5 $218.29   6.441%   $232.3501   $232.35   $232.35   $232.40  
  Purchase #6 $153.82   12.221%   $172.6183   $172.62   $172.60   $172.60  
  Purchase #7 $95.40   12.869%   $107.677   $107.68   $107.70   $107.70  
  7 purchase totals = $1,077.76       $1,193.3911   $1,193.39   $1,193.40   $1,193.50