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 $64.96   5.181%   $68.3256   $68.33   $68.35   $68.30  
  Purchase #2 $234.39   12.228%   $263.0512   $263.05   $263.05   $263.10  
  Purchase #3 $69.26   3.338%   $71.5719   $71.57   $71.55   $71.60  
  Purchase #4 $178.73   5.314%   $188.2277   $188.23   $188.25   $188.20  
  Purchase #5 $60.43   6.170%   $64.1585   $64.16   $64.15   $64.20  
  Purchase #6 $214.80   10.595%   $237.5581   $237.56   $237.55   $237.60  
  Purchase #7 $130.25   5.660%   $137.6222   $137.62   $137.60   $137.60  
  7 purchase totals = $952.82       $1,030.5152   $1,030.52   $1,030.50   $1,030.60