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 $84.68   9.836%   $93.0091   $93.01   $93.00   $93.00  
  Purchase #2 $38.57   12.392%   $43.3496   $43.35   $43.35   $43.30  
  Purchase #3 $98.67   7.660%   $106.2281   $106.23   $106.25   $106.20  
  Purchase #4 $45.82   3.869%   $47.5928   $47.59   $47.60   $47.60  
  Purchase #5 $85.47   9.646%   $93.7144   $93.71   $93.70   $93.70  
  Purchase #6 $124.62   8.230%   $134.8762   $134.88   $134.90   $134.90  
  Purchase #7 $226.41   7.260%   $242.8474   $242.85   $242.85   $242.80  
  7 purchase totals = $704.24       $761.6176   $761.62   $761.65   $761.50