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 $17.96   5.330%   $18.9173   $18.92   $18.90   $18.90  
  Purchase #2 $107.28   13.517%   $121.781   $121.78   $121.80   $121.80  
  Purchase #3 $182.95   12.255%   $205.3705   $205.37   $205.35   $205.40  
  Purchase #4 $238.87   5.653%   $252.3733   $252.37   $252.35   $252.40  
  Purchase #5 $161.61   13.702%   $183.7538   $183.75   $183.75   $183.80  
  Purchase #6 $20.28   5.574%   $21.4104   $21.41   $21.40   $21.40  
  Purchase #7 $117.79   4.850%   $123.5028   $123.50   $123.50   $123.50  
  7 purchase totals = $846.74       $927.1091   $927.10   $927.05   $927.20