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 $62.71   9.489%   $68.6606   $68.66   $68.65   $68.70  
  Purchase #2 $198.88   12.195%   $223.1334   $223.13   $223.15   $223.10  
  Purchase #3 $39.56   11.608%   $44.1521   $44.15   $44.15   $44.20  
  Purchase #4 $55.42   5.623%   $58.5363   $58.54   $58.55   $58.50  
  Purchase #5 $208.67   8.430%   $226.2609   $226.26   $226.25   $226.30  
  Purchase #6 $10.83   3.198%   $11.1763   $11.18   $11.20   $11.20  
  Purchase #7 $23.70   5.291%   $24.954   $24.95   $24.95   $25.00  
  7 purchase totals = $599.77       $656.8736   $656.87   $656.90   $657.00