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 $61.99   11.323%   $69.0091   $69.01   $69.00   $69.00  
  Purchase #2 $190.92   11.239%   $212.3775   $212.38   $212.40   $212.40  
  Purchase #3 $36.32   6.151%   $38.554   $38.55   $38.55   $38.60  
  Purchase #4 $8.80   12.181%   $9.8719   $9.87   $9.85   $9.90  
  Purchase #5 $50.54   4.836%   $52.9841   $52.98   $53.00   $53.00  
  Purchase #6 $17.56   6.504%   $18.7021   $18.70   $18.70   $18.70  
  Purchase #7 $130.90   12.783%   $147.6329   $147.63   $147.65   $147.60  
  7 purchase totals = $497.03       $549.1316   $549.12   $549.15   $549.20