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 $228.98   9.169%   $249.9752   $249.98   $250.00   $250.00  
  Purchase #2 $90.88   6.421%   $96.7154   $96.72   $96.70   $96.70  
  Purchase #3 $75.86   5.463%   $80.0042   $80.00   $80.00   $80.00  
  Purchase #4 $55.52   11.224%   $61.7516   $61.75   $61.75   $61.80  
  Purchase #5 $227.84   13.542%   $258.6941   $258.69   $258.70   $258.70  
  Purchase #6 $231.94   12.675%   $261.3384   $261.34   $261.35   $261.30  
  Purchase #7 $110.72   6.791%   $118.239   $118.24   $118.25   $118.20  
  7 purchase totals = $1,021.74       $1,126.7179   $1,126.72   $1,126.75   $1,126.70