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 $61.85   12.366%   $69.4984   $69.50   $69.50   $69.50  
  Purchase #2 $229.50   3.776%   $238.1659   $238.17   $238.15   $238.20  
  Purchase #3 $225.79   8.467%   $244.9076   $244.91   $244.90   $244.90  
  Purchase #4 $32.96   12.853%   $37.1963   $37.20   $37.20   $37.20  
  Purchase #5 $178.96   7.845%   $192.9994   $193.00   $193.00   $193.00  
  Purchase #6 $67.42   13.373%   $76.4361   $76.44   $76.45   $76.40  
  Purchase #7 $82.40   8.823%   $89.6702   $89.67   $89.65   $89.70  
  7 purchase totals = $878.88       $948.8739   $948.89   $948.85   $948.90