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 $119.84   5.147%   $126.0082   $126.01   $126.00   $126.00  
  Purchase #2 $194.44   3.202%   $200.666   $200.67   $200.65   $200.70  
  Purchase #3 $79.99   7.562%   $86.0388   $86.04   $86.05   $86.00  
  Purchase #4 $38.75   7.159%   $41.5241   $41.52   $41.50   $41.50  
  Purchase #5 $17.79   8.471%   $19.297   $19.30   $19.30   $19.30  
  Purchase #6 $160.63   8.538%   $174.3446   $174.34   $174.35   $174.30  
  Purchase #7 $213.84   8.250%   $231.4818   $231.48   $231.50   $231.50  
  7 purchase totals = $825.28       $879.3605   $879.36   $879.35   $879.30