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 $228.85   9.137%   $249.76   $249.76   $249.75   $249.80  
  Purchase #2 $215.49   9.453%   $235.8603   $235.86   $235.85   $235.90  
  Purchase #3 $169.74   3.266%   $175.2837   $175.28   $175.30   $175.30  
  Purchase #4 $245.52   9.704%   $269.3453   $269.35   $269.35   $269.30  
  Purchase #5 $219.63   8.834%   $239.0321   $239.03   $239.05   $239.00  
  Purchase #6 $66.86   8.333%   $72.4314   $72.43   $72.45   $72.40  
  Purchase #7 $80.47   12.656%   $90.6543   $90.65   $90.65   $90.70  
  7 purchase totals = $1,226.56       $1,332.3671   $1,332.36   $1,332.40   $1,332.40