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 $243.72   10.653%   $269.6835   $269.68   $269.70   $269.70  
  Purchase #2 $94.87   13.289%   $107.4773   $107.48   $107.50   $107.50  
  Purchase #3 $202.44   3.818%   $210.1692   $210.17   $210.15   $210.20  
  Purchase #4 $26.60   11.842%   $29.75   $29.75   $29.75   $29.80  
  Purchase #5 $49.66   11.810%   $55.5248   $55.52   $55.50   $55.50  
  Purchase #6 $240.73   8.788%   $261.8854   $261.89   $261.90   $261.90  
  Purchase #7 $73.32   9.623%   $80.3756   $80.38   $80.40   $80.40  
  7 purchase totals = $931.34       $1,014.8658   $1,014.87   $1,014.90   $1,015.00