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 $138.44   13.360%   $156.9356   $156.94   $156.95   $156.90  
  Purchase #2 $92.87   4.404%   $96.96   $96.96   $96.95   $97.00  
  Purchase #3 $93.63   11.650%   $104.5379   $104.54   $104.55   $104.50  
  Purchase #4 $163.76   6.837%   $174.9563   $174.96   $174.95   $175.00  
  Purchase #5 $11.55   12.817%   $13.0304   $13.03   $13.05   $13.00  
  Purchase #6 $219.30   12.446%   $246.5941   $246.59   $246.60   $246.60  
  Purchase #7 $59.79   9.610%   $65.5358   $65.54   $65.55   $65.50  
  7 purchase totals = $779.34       $858.5501   $858.56   $858.60   $858.50