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 $152.79   8.763%   $166.179   $166.18   $166.20   $166.20  
  Purchase #2 $77.85   13.440%   $88.313   $88.31   $88.30   $88.30  
  Purchase #3 $82.27   5.457%   $86.7595   $86.76   $86.75   $86.80  
  Purchase #4 $182.82   12.350%   $205.3983   $205.40   $205.40   $205.40  
  Purchase #5 $27.78   12.119%   $31.1467   $31.15   $31.15   $31.10  
  Purchase #6 $136.30   4.193%   $142.0151   $142.02   $142.00   $142.00  
  Purchase #7 $234.34   7.446%   $251.789   $251.79   $251.80   $251.80  
  7 purchase totals = $894.15       $971.6006   $971.61   $971.60   $971.60