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 $235.45   11.545%   $262.6327   $262.63   $262.65   $262.60  
  Purchase #2 $76.51   4.694%   $80.1014   $80.10   $80.10   $80.10  
  Purchase #3 $207.57   6.280%   $220.6054   $220.61   $220.60   $220.60  
  Purchase #4 $234.87   10.241%   $258.923   $258.92   $258.90   $258.90  
  Purchase #5 $203.49   10.660%   $225.182   $225.18   $225.20   $225.20  
  Purchase #6 $33.84   6.122%   $35.9117   $35.91   $35.90   $35.90  
  Purchase #7 $222.84   12.380%   $250.4276   $250.43   $250.45   $250.40  
  7 purchase totals = $1,214.57       $1,333.7838   $1,333.78   $1,333.80   $1,333.70