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 $64.79   13.243%   $73.3701   $73.37   $73.35   $73.40  
  Purchase #2 $193.63   9.305%   $211.6473   $211.65   $211.65   $211.60  
  Purchase #3 $104.61   10.640%   $115.7405   $115.74   $115.75   $115.70  
  Purchase #4 $170.26   3.153%   $175.6283   $175.63   $175.65   $175.60  
  Purchase #5 $81.46   3.862%   $84.606   $84.61   $84.60   $84.60  
  Purchase #6 $159.87   3.578%   $165.5901   $165.59   $165.60   $165.60  
  Purchase #7 $190.52   13.622%   $216.4726   $216.47   $216.45   $216.50  
  7 purchase totals = $965.14       $1,043.0549   $1,043.06   $1,043.05   $1,043.00