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 $129.93   11.361%   $144.6913   $144.69   $144.70   $144.70  
  Purchase #2 $113.73   9.238%   $124.2364   $124.24   $124.25   $124.20  
  Purchase #3 $58.25   11.801%   $65.1241   $65.12   $65.10   $65.10  
  Purchase #4 $246.62   6.356%   $262.2952   $262.30   $262.30   $262.30  
  Purchase #5 $141.44   8.754%   $153.8217   $153.82   $153.80   $153.80  
  Purchase #6 $80.81   7.192%   $86.6219   $86.62   $86.60   $86.60  
  Purchase #7 $161.46   8.741%   $175.5732   $175.57   $175.55   $175.60  
  7 purchase totals = $932.24       $1,012.3638   $1,012.36   $1,012.30   $1,012.30