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 $203.99   8.562%   $221.4556   $221.46   $221.45   $221.50  
  Purchase #2 $153.57   11.588%   $171.3657   $171.37   $171.35   $171.40  
  Purchase #3 $212.98   5.593%   $224.892   $224.89   $224.90   $224.90  
  Purchase #4 $13.40   4.753%   $14.0369   $14.04   $14.05   $14.00  
  Purchase #5 $190.42   4.812%   $199.583   $199.58   $199.60   $199.60  
  Purchase #6 $223.45   8.550%   $242.555   $242.56   $242.55   $242.60  
  Purchase #7 $113.76   4.745%   $119.1579   $119.16   $119.15   $119.20  
  7 purchase totals = $1,111.57       $1,193.0461   $1,193.06   $1,193.05   $1,193.20