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 $62.56   11.666%   $69.8582   $69.86   $69.85   $69.90  
  Purchase #2 $223.52   12.413%   $251.2655   $251.27   $251.25   $251.30  
  Purchase #3 $178.55   7.755%   $192.3966   $192.40   $192.40   $192.40  
  Purchase #4 $73.93   13.617%   $83.997   $84.00   $84.00   $84.00  
  Purchase #5 $151.59   10.613%   $167.6782   $167.68   $167.70   $167.70  
  Purchase #6 $225.40   3.649%   $233.6248   $233.62   $233.60   $233.60  
  Purchase #7 $28.40   4.810%   $29.766   $29.77   $29.75   $29.80  
  7 purchase totals = $943.95       $1,028.5863   $1,028.60   $1,028.55   $1,028.70