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 $190.99   4.818%   $200.1919   $200.19   $200.20   $200.20  
  Purchase #2 $59.99   12.181%   $67.2974   $67.30   $67.30   $67.30  
  Purchase #3 $114.30   6.314%   $121.5169   $121.52   $121.50   $121.50  
  Purchase #4 $20.59   6.523%   $21.9331   $21.93   $21.95   $21.90  
  Purchase #5 $245.55   4.147%   $255.733   $255.73   $255.75   $255.70  
  Purchase #6 $9.93   10.847%   $11.0071   $11.01   $11.00   $11.00  
  Purchase #7 $61.48   3.819%   $63.8279   $63.83   $63.85   $63.80  
  7 purchase totals = $702.83       $741.5073   $741.51   $741.55   $741.40