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 $60.62   9.595%   $66.4365   $66.44   $66.45   $66.40  
  Purchase #2 $194.87   3.617%   $201.9184   $201.92   $201.90   $201.90  
  Purchase #3 $138.44   5.391%   $145.9033   $145.90   $145.90   $145.90  
  Purchase #4 $78.64   3.445%   $81.3491   $81.35   $81.35   $81.30  
  Purchase #5 $91.32   8.410%   $99   $99.00   $99.00   $99.00  
  Purchase #6 $6.48   13.634%   $7.3635   $7.36   $7.35   $7.40  
  Purchase #7 $187.68   9.831%   $206.1308   $206.13   $206.15   $206.10  
  7 purchase totals = $758.05       $808.1016   $808.10   $808.10   $808.00