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 $178.73   5.213%   $188.0472   $188.05   $188.05   $188.00  
  Purchase #2 $76.85   7.553%   $82.6545   $82.65   $82.65   $82.70  
  Purchase #3 $59.25   10.213%   $65.3012   $65.30   $65.30   $65.30  
  Purchase #4 $136.96   12.801%   $154.4922   $154.49   $154.50   $154.50  
  Purchase #5 $61.59   10.713%   $68.1881   $68.19   $68.20   $68.20  
  Purchase #6 $236.35   11.217%   $262.8614   $262.86   $262.85   $262.90  
  Purchase #7 $233.48   5.386%   $246.0552   $246.06   $246.05   $246.10  
  7 purchase totals = $983.21       $1,067.5998   $1,067.60   $1,067.60   $1,067.70