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 $210.93   10.628%   $233.3476   $233.35   $233.35   $233.30  
  Purchase #2 $113.74   7.168%   $121.8929   $121.89   $121.90   $121.90  
  Purchase #3 $197.93   9.523%   $216.7789   $216.78   $216.80   $216.80  
  Purchase #4 $52.75   5.544%   $55.6745   $55.67   $55.65   $55.70  
  Purchase #5 $246.79   9.615%   $270.5189   $270.52   $270.50   $270.50  
  Purchase #6 $185.94   3.364%   $192.195   $192.20   $192.20   $192.20  
  Purchase #7 $229.54   12.238%   $257.6311   $257.63   $257.65   $257.60  
  7 purchase totals = $1,237.62       $1,348.0389   $1,348.04   $1,348.05   $1,348.00