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 $54.99   8.354%   $59.5839   $59.58   $59.60   $59.60  
  Purchase #2 $191.49   7.617%   $206.0758   $206.08   $206.10   $206.10  
  Purchase #3 $18.64   3.310%   $19.257   $19.26   $19.25   $19.30  
  Purchase #4 $161.82   3.547%   $167.5598   $167.56   $167.55   $167.60  
  Purchase #5 $183.89   11.609%   $205.2378   $205.24   $205.25   $205.20  
  Purchase #6 $151.35   10.854%   $167.7775   $167.78   $167.80   $167.80  
  Purchase #7 $221.80   13.389%   $251.4968   $251.50   $251.50   $251.50  
  7 purchase totals = $983.98       $1,076.9886   $1,077.00   $1,077.05   $1,077.10