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 $214.65   8.326%   $232.5218   $232.52   $232.50   $232.50  
  Purchase #2 $241.35   13.116%   $273.0055   $273.01   $273.00   $273.00  
  Purchase #3 $119.99   10.139%   $132.1558   $132.16   $132.15   $132.20  
  Purchase #4 $15.89   3.162%   $16.3924   $16.39   $16.40   $16.40  
  Purchase #5 $212.43   4.343%   $221.6558   $221.66   $221.65   $221.70  
  Purchase #6 $129.29   6.766%   $138.0378   $138.04   $138.05   $138.00  
  Purchase #7 $41.28   6.436%   $43.9368   $43.94   $43.95   $43.90  
  7 purchase totals = $974.88       $1,057.7059   $1,057.72   $1,057.70   $1,057.70