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 $173.83   13.748%   $197.7281   $197.73   $197.75   $197.70  
  Purchase #2 $134.48   11.141%   $149.4624   $149.46   $149.45   $149.50  
  Purchase #3 $114.38   5.564%   $120.7441   $120.74   $120.75   $120.70  
  Purchase #4 $57.27   11.715%   $63.9792   $63.98   $64.00   $64.00  
  Purchase #5 $127.69   9.106%   $139.3175   $139.32   $139.30   $139.30  
  Purchase #6 $206.31   6.382%   $219.4767   $219.48   $219.50   $219.50  
  Purchase #7 $216.89   10.471%   $239.6006   $239.60   $239.60   $239.60  
  7 purchase totals = $1,030.85       $1,130.3086   $1,130.31   $1,130.35   $1,130.30