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 $64.64   7.365%   $69.4007   $69.40   $69.40   $69.40  
  Purchase #2 $211.74   10.629%   $234.2458   $234.25   $234.25   $234.20  
  Purchase #3 $203.91   5.311%   $214.7397   $214.74   $214.75   $214.70  
  Purchase #4 $170.88   13.197%   $193.431   $193.43   $193.45   $193.40  
  Purchase #5 $105.57   3.524%   $109.2903   $109.29   $109.30   $109.30  
  Purchase #6 $93.75   9.679%   $102.8241   $102.82   $102.80   $102.80  
  Purchase #7 $41.59   11.354%   $46.3121   $46.31   $46.30   $46.30  
  7 purchase totals = $892.08       $970.2437   $970.24   $970.25   $970.10