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 $139.66   13.617%   $158.6775   $158.68   $158.70   $158.70  
  Purchase #2 $224.36   8.396%   $243.1973   $243.20   $243.20   $243.20  
  Purchase #3 $149.34   12.416%   $167.8821   $167.88   $167.90   $167.90  
  Purchase #4 $240.94   4.792%   $252.4858   $252.49   $252.50   $252.50  
  Purchase #5 $72.39   4.471%   $75.6266   $75.63   $75.65   $75.60  
  Purchase #6 $67.71   3.130%   $69.8293   $69.83   $69.85   $69.80  
  Purchase #7 $55.96   3.597%   $57.9729   $57.97   $57.95   $58.00  
  7 purchase totals = $950.36       $1,025.6715   $1,025.68   $1,025.75   $1,025.70