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 $238.49   12.188%   $267.5572   $267.56   $267.55   $267.60  
  Purchase #2 $176.26   4.244%   $183.7405   $183.74   $183.75   $183.70  
  Purchase #3 $76.80   5.284%   $80.8581   $80.86   $80.85   $80.90  
  Purchase #4 $34.92   6.721%   $37.267   $37.27   $37.25   $37.30  
  Purchase #5 $240.90   8.333%   $260.9742   $260.97   $260.95   $261.00  
  Purchase #6 $96.87   7.315%   $103.956   $103.96   $103.95   $104.00  
  Purchase #7 $115.29   4.379%   $120.3385   $120.34   $120.35   $120.30  
  7 purchase totals = $979.53       $1,054.6915   $1,054.70   $1,054.65   $1,054.80