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 $57.44   3.194%   $59.2746   $59.27   $59.25   $59.30  
  Purchase #2 $22.80   13.573%   $25.8946   $25.89   $25.90   $25.90  
  Purchase #3 $123.54   5.241%   $130.0147   $130.01   $130.00   $130.00  
  Purchase #4 $55.92   13.171%   $63.2852   $63.29   $63.30   $63.30  
  Purchase #5 $211.33   11.508%   $235.6499   $235.65   $235.65   $235.60  
  Purchase #6 $106.37   7.331%   $114.168   $114.17   $114.15   $114.20  
  Purchase #7 $216.66   3.638%   $224.5421   $224.54   $224.55   $224.50  
  7 purchase totals = $794.06       $852.8291   $852.82   $852.80   $852.80