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 $216.95   11.449%   $241.7886   $241.79   $241.80   $241.80  
  Purchase #2 $228.59   7.229%   $245.1148   $245.11   $245.10   $245.10  
  Purchase #3 $84.45   7.335%   $90.6444   $90.64   $90.65   $90.60  
  Purchase #4 $8.92   8.316%   $9.6618   $9.66   $9.65   $9.70  
  Purchase #5 $230.76   11.795%   $257.9781   $257.98   $258.00   $258.00  
  Purchase #6 $80.72   5.637%   $85.2702   $85.27   $85.25   $85.30  
  Purchase #7 $235.98   13.606%   $268.0874   $268.09   $268.10   $268.10  
  7 purchase totals = $1,086.37       $1,198.5453   $1,198.54   $1,198.55   $1,198.60