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 $246.62   11.304%   $274.4979   $274.50   $274.50   $274.50  
  Purchase #2 $234.46   7.630%   $252.3493   $252.35   $252.35   $252.30  
  Purchase #3 $224.89   10.115%   $247.6376   $247.64   $247.65   $247.60  
  Purchase #4 $6.52   7.199%   $6.9894   $6.99   $7.00   $7.00  
  Purchase #5 $220.40   13.557%   $250.2796   $250.28   $250.30   $250.30  
  Purchase #6 $225.26   5.158%   $236.8789   $236.88   $236.90   $236.90  
  Purchase #7 $101.69   11.479%   $113.363   $113.36   $113.35   $113.40  
  7 purchase totals = $1,259.84       $1,381.9957   $1,382.00   $1,382.05   $1,382.00