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 $118.51   10.103%   $130.4831   $130.48   $130.50   $130.50  
  Purchase #2 $65.25   8.581%   $70.8491   $70.85   $70.85   $70.80  
  Purchase #3 $245.85   5.363%   $259.0349   $259.03   $259.05   $259.00  
  Purchase #4 $219.66   4.794%   $230.1905   $230.19   $230.20   $230.20  
  Purchase #5 $226.88   3.127%   $233.9745   $233.97   $233.95   $234.00  
  Purchase #6 $74.69   10.175%   $82.2897   $82.29   $82.30   $82.30  
  Purchase #7 $226.43   3.599%   $234.5792   $234.58   $234.60   $234.60  
  7 purchase totals = $1,177.27       $1,241.4010   $1,241.39   $1,241.45   $1,241.40