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 $91.52   5.746%   $96.7787   $96.78   $96.80   $96.80  
  Purchase #2 $131.41   3.797%   $136.3996   $136.40   $136.40   $136.40  
  Purchase #3 $202.26   12.318%   $227.1744   $227.17   $227.15   $227.20  
  Purchase #4 $224.63   8.832%   $244.4693   $244.47   $244.45   $244.50  
  Purchase #5 $116.28   10.280%   $128.2336   $128.23   $128.25   $128.20  
  Purchase #6 $74.62   7.393%   $80.1367   $80.14   $80.15   $80.10  
  Purchase #7 $134.35   5.353%   $141.5418   $141.54   $141.55   $141.50  
  7 purchase totals = $975.07       $1,054.7341   $1,054.73   $1,054.75   $1,054.70