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 $61.97   9.425%   $67.8107   $67.81   $67.80   $67.80  
  Purchase #2 $232.37   12.301%   $260.9538   $260.95   $260.95   $261.00  
  Purchase #3 $111.89   9.422%   $122.4323   $122.43   $122.45   $122.40  
  Purchase #4 $116.71   5.516%   $123.1477   $123.15   $123.15   $123.10  
  Purchase #5 $97.40   8.494%   $105.6732   $105.67   $105.65   $105.70  
  Purchase #6 $27.81   4.694%   $29.1154   $29.12   $29.10   $29.10  
  Purchase #7 $68.95   13.196%   $78.0486   $78.05   $78.05   $78.00  
  7 purchase totals = $717.10       $787.1817   $787.18   $787.15   $787.10