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 $219.26   8.523%   $237.9475   $237.95   $237.95   $237.90  
  Purchase #2 $156.92   6.187%   $166.6286   $166.63   $166.65   $166.60  
  Purchase #3 $30.96   11.769%   $34.6037   $34.60   $34.60   $34.60  
  Purchase #4 $95.79   4.845%   $100.431   $100.43   $100.45   $100.40  
  Purchase #5 $181.61   8.753%   $197.5063   $197.51   $197.50   $197.50  
  Purchase #6 $115.75   5.442%   $122.0491   $122.05   $122.05   $122.00  
  Purchase #7 $124.74   13.834%   $141.9965   $142.00   $142.00   $142.00  
  7 purchase totals = $925.03       $1,001.1627   $1,001.17   $1,001.20   $1,001.00