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 $149.55   9.136%   $163.2129   $163.21   $163.20   $163.20  
  Purchase #2 $248.36   11.125%   $275.9901   $275.99   $276.00   $276.00  
  Purchase #3 $188.98   7.228%   $202.6395   $202.64   $202.65   $202.60  
  Purchase #4 $213.99   7.704%   $230.4758   $230.48   $230.50   $230.50  
  Purchase #5 $118.91   4.607%   $124.3882   $124.39   $124.40   $124.40  
  Purchase #6 $61.47   12.841%   $69.3634   $69.36   $69.35   $69.40  
  Purchase #7 $11.66   9.492%   $12.7668   $12.77   $12.75   $12.80  
  7 purchase totals = $992.92       $1,078.8367   $1,078.84   $1,078.85   $1,078.90