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 $118.59   6.691%   $126.5249   $126.52   $126.50   $126.50  
  Purchase #2 $166.76   11.691%   $186.2559   $186.26   $186.25   $186.30  
  Purchase #3 $196.74   3.160%   $202.957   $202.96   $202.95   $203.00  
  Purchase #4 $219.25   4.420%   $228.9409   $228.94   $228.95   $228.90  
  Purchase #5 $176.85   9.409%   $193.4898   $193.49   $193.50   $193.50  
  Purchase #6 $191.76   7.572%   $206.2801   $206.28   $206.30   $206.30  
  Purchase #7 $51.71   13.264%   $58.5688   $58.57   $58.55   $58.60  
  7 purchase totals = $1,121.66       $1,203.0174   $1,203.02   $1,203.00   $1,203.10