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 $47.32   6.309%   $50.3054   $50.31   $50.30   $50.30  
  Purchase #2 $218.30   11.340%   $243.0552   $243.06   $243.05   $243.10  
  Purchase #3 $40.35   3.380%   $41.7138   $41.71   $41.70   $41.70  
  Purchase #4 $235.68   11.671%   $263.1862   $263.19   $263.20   $263.20  
  Purchase #5 $22.70   3.393%   $23.4702   $23.47   $23.45   $23.50  
  Purchase #6 $165.83   12.109%   $185.9104   $185.91   $185.90   $185.90  
  Purchase #7 $204.91   7.745%   $220.7803   $220.78   $220.80   $220.80  
  7 purchase totals = $935.09       $1,028.4215   $1,028.43   $1,028.40   $1,028.50