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 $207.61   12.835%   $234.2567   $234.26   $234.25   $234.30  
  Purchase #2 $220.43   9.783%   $241.9947   $241.99   $242.00   $242.00  
  Purchase #3 $215.52   12.332%   $242.0979   $242.10   $242.10   $242.10  
  Purchase #4 $101.89   12.205%   $114.3257   $114.33   $114.35   $114.30  
  Purchase #5 $134.27   9.772%   $147.3909   $147.39   $147.40   $147.40  
  Purchase #6 $70.55   4.697%   $73.8637   $73.86   $73.85   $73.90  
  Purchase #7 $175.35   3.134%   $180.8455   $180.85   $180.85   $180.80  
  7 purchase totals = $1,125.62       $1,234.7751   $1,234.78   $1,234.80   $1,234.80