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 $233.77   8.205%   $252.9508   $252.95   $252.95   $253.00  
  Purchase #2 $21.58   8.104%   $23.3288   $23.33   $23.35   $23.30  
  Purchase #3 $144.92   13.869%   $165.019   $165.02   $165.00   $165.00  
  Purchase #4 $69.61   9.192%   $76.0086   $76.01   $76.00   $76.00  
  Purchase #5 $206.86   5.866%   $218.9944   $218.99   $219.00   $219.00  
  Purchase #6 $246.70   12.395%   $277.2785   $277.28   $277.30   $277.30  
  Purchase #7 $217.42   9.486%   $238.0445   $238.04   $238.05   $238.00  
  7 purchase totals = $1,140.86       $1,251.6246   $1,251.62   $1,251.65   $1,251.60