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 $212.82   12.261%   $238.9139   $238.91   $238.90   $238.90  
  Purchase #2 $188.94   8.117%   $204.2763   $204.28   $204.30   $204.30  
  Purchase #3 $139.84   8.697%   $152.0019   $152.00   $152.00   $152.00  
  Purchase #4 $97.32   4.444%   $101.6449   $101.64   $101.65   $101.60  
  Purchase #5 $202.42   5.125%   $212.794   $212.79   $212.80   $212.80  
  Purchase #6 $68.81   5.545%   $72.6255   $72.63   $72.65   $72.60  
  Purchase #7 $23.84   11.662%   $26.6202   $26.62   $26.60   $26.60  
  7 purchase totals = $933.99       $1,008.8767   $1,008.87   $1,008.90   $1,008.80