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 $186.61   7.155%   $199.9619   $199.96   $199.95   $200.00  
  Purchase #2 $233.75   12.615%   $263.2376   $263.24   $263.25   $263.20  
  Purchase #3 $10.79   9.818%   $11.8494   $11.85   $11.85   $11.80  
  Purchase #4 $24.61   9.283%   $26.8945   $26.89   $26.90   $26.90  
  Purchase #5 $180.95   5.614%   $191.1085   $191.11   $191.10   $191.10  
  Purchase #6 $76.26   13.609%   $86.6382   $86.64   $86.65   $86.60  
  Purchase #7 $240.77   13.517%   $273.3149   $273.31   $273.30   $273.30  
  7 purchase totals = $953.74       $1,053.0050   $1,053.00   $1,053.00   $1,052.90