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 $185.53   4.118%   $193.1701   $193.17   $193.15   $193.20  
  Purchase #2 $143.92   6.110%   $152.7135   $152.71   $152.70   $152.70  
  Purchase #3 $141.31   5.217%   $148.6821   $148.68   $148.70   $148.70  
  Purchase #4 $237.58   6.617%   $253.3007   $253.30   $253.30   $253.30  
  Purchase #5 $25.48   7.453%   $27.379   $27.38   $27.40   $27.40  
  Purchase #6 $230.89   9.364%   $252.5105   $252.51   $252.50   $252.50  
  Purchase #7 $52.36   11.776%   $58.5259   $58.53   $58.55   $58.50  
  7 purchase totals = $1,017.07       $1,086.2818   $1,086.28   $1,086.30   $1,086.30