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 $215.90   13.827%   $245.7525   $245.75   $245.75   $245.80  
  Purchase #2 $5.65   3.827%   $5.8662   $5.87   $5.85   $5.90  
  Purchase #3 $112.88   6.686%   $120.4272   $120.43   $120.45   $120.40  
  Purchase #4 $143.52   4.851%   $150.4822   $150.48   $150.50   $150.50  
  Purchase #5 $175.27   13.348%   $198.665   $198.67   $198.65   $198.70  
  Purchase #6 $210.67   11.758%   $235.4406   $235.44   $235.45   $235.40  
  Purchase #7 $85.55   7.678%   $92.1185   $92.12   $92.10   $92.10  
  7 purchase totals = $949.44       $1,048.7522   $1,048.76   $1,048.75   $1,048.80