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 $141.92   13.440%   $160.994   $160.99   $161.00   $161.00  
  Purchase #2 $184.54   6.114%   $195.8228   $195.82   $195.80   $195.80  
  Purchase #3 $226.64   10.162%   $249.6712   $249.67   $249.65   $249.70  
  Purchase #4 $96.31   11.833%   $107.7064   $107.71   $107.70   $107.70  
  Purchase #5 $104.76   13.655%   $119.065   $119.07   $119.05   $119.10  
  Purchase #6 $141.95   3.708%   $147.2135   $147.21   $147.20   $147.20  
  Purchase #7 $71.45   6.280%   $75.9371   $75.94   $75.95   $75.90  
  7 purchase totals = $967.57       $1,056.4100   $1,056.41   $1,056.35   $1,056.40