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 $76.52   12.507%   $86.0904   $86.09   $86.10   $86.10  
  Purchase #2 $85.95   6.291%   $91.3571   $91.36   $91.35   $91.40  
  Purchase #3 $144.93   8.517%   $157.2737   $157.27   $157.25   $157.30  
  Purchase #4 $109.40   7.817%   $117.9518   $117.95   $117.95   $118.00  
  Purchase #5 $223.86   8.468%   $242.8165   $242.82   $242.80   $242.80  
  Purchase #6 $196.35   13.692%   $223.2342   $223.23   $223.25   $223.20  
  Purchase #7 $95.52   11.201%   $106.2192   $106.22   $106.20   $106.20  
  7 purchase totals = $932.53       $1,024.9429   $1,024.94   $1,024.90   $1,025.00