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 $242.58   11.243%   $269.8533   $269.85   $269.85   $269.90  
  Purchase #2 $147.81   7.812%   $159.3569   $159.36   $159.35   $159.40  
  Purchase #3 $33.85   12.693%   $38.1466   $38.15   $38.15   $38.10  
  Purchase #4 $66.85   11.836%   $74.7624   $74.76   $74.75   $74.80  
  Purchase #5 $24.54   4.144%   $25.5569   $25.56   $25.55   $25.60  
  Purchase #6 $73.92   3.466%   $76.4821   $76.48   $76.50   $76.50  
  Purchase #7 $112.55   9.745%   $123.518   $123.52   $123.50   $123.50  
  7 purchase totals = $702.10       $767.6762   $767.68   $767.65   $767.80