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 $188.40   10.142%   $207.5075   $207.51   $207.50   $207.50  
  Purchase #2 $245.74   4.418%   $256.5968   $256.60   $256.60   $256.60  
  Purchase #3 $60.41   7.308%   $64.8248   $64.82   $64.80   $64.80  
  Purchase #4 $156.64   11.217%   $174.2103   $174.21   $174.20   $174.20  
  Purchase #5 $140.61   9.214%   $153.5658   $153.57   $153.55   $153.60  
  Purchase #6 $229.98   9.142%   $251.0048   $251.00   $251.00   $251.00  
  Purchase #7 $81.32   6.770%   $86.8254   $86.83   $86.85   $86.80  
  7 purchase totals = $1,103.10       $1,194.5354   $1,194.54   $1,194.50   $1,194.50