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 $152.88   9.781%   $167.8332   $167.83   $167.85   $167.80  
  Purchase #2 $5.95   5.147%   $6.2562   $6.26   $6.25   $6.30  
  Purchase #3 $250.46   4.162%   $260.8841   $260.88   $260.90   $260.90  
  Purchase #4 $71.62   7.561%   $77.0352   $77.04   $77.05   $77.00  
  Purchase #5 $197.79   3.721%   $205.1498   $205.15   $205.15   $205.10  
  Purchase #6 $206.53   13.768%   $234.9651   $234.97   $234.95   $235.00  
  Purchase #7 $67.67   3.852%   $70.2766   $70.28   $70.30   $70.30  
  7 purchase totals = $952.90       $1,022.4002   $1,022.41   $1,022.45   $1,022.40